powerpc: Improve resolution of VDSO clock_gettime
Currently the clock_gettime implementation in the VDSO produces a result with microsecond resolution for the cases that are handled without a system call, i.e. CLOCK_REALTIME and CLOCK_MONOTONIC. The nanoseconds field of the result is obtained by computing a microseconds value and multiplying by 1000. This changes the code in the VDSO to do the computation for clock_gettime with nanosecond resolution. That means that the resolution of the result will ultimately depend on the timebase frequency. Because the timestamp in the VDSO datapage (stamp_xsec, the real time corresponding to the timebase count in tb_orig_stamp) is in units of 2^-20 seconds, it doesn't have sufficient resolution for computing a result with nanosecond resolution. Therefore this adds a copy of xtime to the VDSO datapage and updates it in update_gtod() along with the other time-related fields. Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Paul Mackerras
Родитель
c73049f6aa
Коммит
597bc5c00b
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@ -39,6 +39,7 @@
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#ifndef __ASSEMBLY__
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#include <linux/unistd.h>
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#include <linux/time.h>
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#define SYSCALL_MAP_SIZE ((__NR_syscalls + 31) / 32)
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@ -83,6 +84,7 @@ struct vdso_data {
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__u32 icache_log_block_size; /* L1 i-cache log block size */
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__s32 wtom_clock_sec; /* Wall to monotonic clock */
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__s32 wtom_clock_nsec;
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struct timespec stamp_xtime; /* xtime as at tb_orig_stamp */
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__u32 syscall_map_64[SYSCALL_MAP_SIZE]; /* map of syscalls */
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__u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
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};
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@ -102,6 +104,7 @@ struct vdso_data {
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__u32 tz_dsttime; /* Type of dst correction 0x5C */
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__s32 wtom_clock_sec; /* Wall to monotonic clock */
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__s32 wtom_clock_nsec;
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struct timespec stamp_xtime; /* xtime as at tb_orig_stamp */
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__u32 syscall_map_32[SYSCALL_MAP_SIZE]; /* map of syscalls */
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__u32 dcache_block_size; /* L1 d-cache block size */
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__u32 icache_block_size; /* L1 i-cache block size */
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@ -306,6 +306,7 @@ int main(void)
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DEFINE(CFG_SYSCALL_MAP32, offsetof(struct vdso_data, syscall_map_32));
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DEFINE(WTOM_CLOCK_SEC, offsetof(struct vdso_data, wtom_clock_sec));
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DEFINE(WTOM_CLOCK_NSEC, offsetof(struct vdso_data, wtom_clock_nsec));
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DEFINE(STAMP_XTIME, offsetof(struct vdso_data, stamp_xtime));
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DEFINE(CFG_ICACHE_BLOCKSZ, offsetof(struct vdso_data, icache_block_size));
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DEFINE(CFG_DCACHE_BLOCKSZ, offsetof(struct vdso_data, dcache_block_size));
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DEFINE(CFG_ICACHE_LOGBLOCKSZ, offsetof(struct vdso_data, icache_log_block_size));
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@ -456,6 +456,7 @@ static inline void update_gtod(u64 new_tb_stamp, u64 new_stamp_xsec,
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vdso_data->tb_to_xs = new_tb_to_xs;
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vdso_data->wtom_clock_sec = wall_to_monotonic.tv_sec;
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vdso_data->wtom_clock_nsec = wall_to_monotonic.tv_nsec;
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vdso_data->stamp_xtime = xtime;
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smp_wmb();
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++(vdso_data->tb_update_count);
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}
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@ -16,6 +16,13 @@
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#include <asm/asm-offsets.h>
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#include <asm/unistd.h>
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/* Offset for the low 32-bit part of a field of long type */
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#ifdef CONFIG_PPC64
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#define LOPART 4
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#else
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#define LOPART 0
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#endif
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.text
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/*
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* Exact prototype of gettimeofday
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@ -90,101 +97,53 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
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mflr r12 /* r12 saves lr */
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.cfi_register lr,r12
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mr r10,r3 /* r10 saves id */
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mr r11,r4 /* r11 saves tp */
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bl __get_datapage@local /* get data page */
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mr r9,r3 /* datapage ptr in r9 */
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beq cr1,50f /* if monotonic -> jump there */
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/*
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* CLOCK_REALTIME
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*/
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bl __do_get_xsec@local /* get xsec from tb & kernel */
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bne- 98f /* out of line -> do syscall */
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/* seconds are xsec >> 20 */
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rlwinm r5,r4,12,20,31
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rlwimi r5,r3,12,0,19
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stw r5,TSPC32_TV_SEC(r11)
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/* get remaining xsec and convert to nsec. we scale
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* up remaining xsec by 12 bits and get the top 32 bits
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* of the multiplication, then we multiply by 1000
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*/
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rlwinm r5,r4,12,0,19
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lis r6,1000000@h
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ori r6,r6,1000000@l
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mulhwu r5,r5,r6
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mulli r5,r5,1000
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stw r5,TSPC32_TV_NSEC(r11)
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mtlr r12
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crclr cr0*4+so
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li r3,0
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blr
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50: bl __do_get_tspec@local /* get sec/nsec from tb & kernel */
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bne cr1,80f /* not monotonic -> all done */
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/*
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* CLOCK_MONOTONIC
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*/
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50: bl __do_get_xsec@local /* get xsec from tb & kernel */
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bne- 98f /* out of line -> do syscall */
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/* seconds are xsec >> 20 */
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rlwinm r6,r4,12,20,31
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rlwimi r6,r3,12,0,19
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/* get remaining xsec and convert to nsec. we scale
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* up remaining xsec by 12 bits and get the top 32 bits
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* of the multiplication, then we multiply by 1000
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*/
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rlwinm r7,r4,12,0,19
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lis r5,1000000@h
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ori r5,r5,1000000@l
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mulhwu r7,r7,r5
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mulli r7,r7,1000
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/* now we must fixup using wall to monotonic. We need to snapshot
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* that value and do the counter trick again. Fortunately, we still
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* have the counter value in r8 that was returned by __do_get_xsec.
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* At this point, r6,r7 contain our sec/nsec values, r3,r4 and r5
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* can be used
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* At this point, r3,r4 contain our sec/nsec values, r5 and r6
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* can be used, r7 contains NSEC_PER_SEC.
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*/
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lwz r3,WTOM_CLOCK_SEC(r9)
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lwz r4,WTOM_CLOCK_NSEC(r9)
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lwz r5,WTOM_CLOCK_SEC(r9)
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lwz r6,WTOM_CLOCK_NSEC(r9)
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/* We now have our result in r3,r4. We create a fake dependency
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* on that result and re-check the counter
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/* We now have our offset in r5,r6. We create a fake dependency
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* on that value and re-check the counter
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*/
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or r5,r4,r3
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xor r0,r5,r5
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or r0,r6,r5
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xor r0,r0,r0
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add r9,r9,r0
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#ifdef CONFIG_PPC64
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lwz r0,(CFG_TB_UPDATE_COUNT+4)(r9)
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#else
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lwz r0,(CFG_TB_UPDATE_COUNT)(r9)
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#endif
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lwz r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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cmpl cr0,r8,r0 /* check if updated */
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bne- 50b
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/* Calculate and store result. Note that this mimmics the C code,
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/* Calculate and store result. Note that this mimics the C code,
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* which may cause funny results if nsec goes negative... is that
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* possible at all ?
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*/
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add r3,r3,r6
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add r4,r4,r7
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lis r5,NSEC_PER_SEC@h
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ori r5,r5,NSEC_PER_SEC@l
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cmpl cr0,r4,r5
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cmpli cr1,r4,0
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add r3,r3,r5
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add r4,r4,r6
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cmpw cr0,r4,r7
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cmpwi cr1,r4,0
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blt 1f
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subf r4,r5,r4
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subf r4,r7,r4
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addi r3,r3,1
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1: bge cr1,1f
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1: bge cr1,80f
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addi r3,r3,-1
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add r4,r4,r5
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1: stw r3,TSPC32_TV_SEC(r11)
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add r4,r4,r7
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80: stw r3,TSPC32_TV_SEC(r11)
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stw r4,TSPC32_TV_NSEC(r11)
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mtlr r12
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@ -195,10 +154,6 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
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/*
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* syscall fallback
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*/
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98:
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mtlr r12
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mr r3,r10
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mr r4,r11
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99:
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li r0,__NR_clock_gettime
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sc
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@ -254,11 +209,7 @@ __do_get_xsec:
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/* Check for update count & load values. We use the low
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* order 32 bits of the update count
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*/
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#ifdef CONFIG_PPC64
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1: lwz r8,(CFG_TB_UPDATE_COUNT+4)(r9)
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#else
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1: lwz r8,(CFG_TB_UPDATE_COUNT)(r9)
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#endif
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1: lwz r8,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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andi. r0,r8,1 /* pending update ? loop */
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bne- 1b
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xor r0,r8,r8 /* create dependency */
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@ -305,11 +256,7 @@ __do_get_xsec:
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or r6,r4,r3
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xor r0,r6,r6
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add r9,r9,r0
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#ifdef CONFIG_PPC64
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lwz r0,(CFG_TB_UPDATE_COUNT+4)(r9)
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#else
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lwz r0,(CFG_TB_UPDATE_COUNT)(r9)
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#endif
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lwz r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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cmpl cr0,r8,r0 /* check if updated */
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bne- 1b
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@ -322,3 +269,98 @@ __do_get_xsec:
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*/
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3: blr
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.cfi_endproc
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/*
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* This is the core of clock_gettime(), it returns the current
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* time in seconds and nanoseconds in r3 and r4.
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* It expects the datapage ptr in r9 and doesn't clobber it.
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* It clobbers r0, r5, r6, r10 and returns NSEC_PER_SEC in r7.
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* On return, r8 contains the counter value that can be reused.
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* This clobbers cr0 but not any other cr field.
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*/
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__do_get_tspec:
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.cfi_startproc
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/* Check for update count & load values. We use the low
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* order 32 bits of the update count
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*/
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1: lwz r8,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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andi. r0,r8,1 /* pending update ? loop */
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bne- 1b
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xor r0,r8,r8 /* create dependency */
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add r9,r9,r0
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/* Load orig stamp (offset to TB) */
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lwz r5,CFG_TB_ORIG_STAMP(r9)
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lwz r6,(CFG_TB_ORIG_STAMP+4)(r9)
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/* Get a stable TB value */
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2: mftbu r3
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mftbl r4
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mftbu r0
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cmpl cr0,r3,r0
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bne- 2b
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/* Subtract tb orig stamp and shift left 12 bits.
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*/
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subfc r7,r6,r4
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subfe r0,r5,r3
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slwi r0,r0,12
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rlwimi. r0,r7,12,20,31
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slwi r7,r7,12
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/* Load scale factor & do multiplication */
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lwz r5,CFG_TB_TO_XS(r9) /* load values */
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lwz r6,(CFG_TB_TO_XS+4)(r9)
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mulhwu r3,r7,r6
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mullw r10,r7,r5
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mulhwu r4,r7,r5
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addc r10,r3,r10
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li r3,0
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beq+ 4f /* skip high part computation if 0 */
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mulhwu r3,r0,r5
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mullw r7,r0,r5
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mulhwu r5,r0,r6
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mullw r6,r0,r6
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adde r4,r4,r7
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addze r3,r3
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addc r4,r4,r5
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addze r3,r3
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addc r10,r10,r6
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4: addze r4,r4 /* add in carry */
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lis r7,NSEC_PER_SEC@h
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ori r7,r7,NSEC_PER_SEC@l
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mulhwu r4,r4,r7 /* convert to nanoseconds */
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/* At this point, we have seconds & nanoseconds since the xtime
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* stamp in r3+CA and r4. Load & add the xtime stamp.
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*/
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#ifdef CONFIG_PPC64
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lwz r5,STAMP_XTIME+TSPC64_TV_SEC+LOPART(r9)
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lwz r6,STAMP_XTIME+TSPC64_TV_NSEC+LOPART(r9)
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#else
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lwz r5,STAMP_XTIME+TSPC32_TV_SEC(r9)
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lwz r6,STAMP_XTIME+TSPC32_TV_NSEC(r9)
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#endif
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add r4,r4,r6
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adde r3,r3,r5
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/* We now have our result in r3,r4. We create a fake dependency
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* on that result and re-check the counter
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*/
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or r6,r4,r3
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xor r0,r6,r6
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add r9,r9,r0
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lwz r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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cmpl cr0,r8,r0 /* check if updated */
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bne- 1b
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/* check for nanosecond overflow and adjust if necessary */
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cmpw r4,r7
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bltlr /* all done if no overflow */
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subf r4,r7,r4 /* adjust if overflow */
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addi r3,r3,1
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blr
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.cfi_endproc
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@ -75,90 +75,49 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
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mflr r12 /* r12 saves lr */
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.cfi_register lr,r12
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mr r10,r3 /* r10 saves id */
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mr r11,r4 /* r11 saves tp */
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bl V_LOCAL_FUNC(__get_datapage) /* get data page */
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beq cr1,50f /* if monotonic -> jump there */
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/*
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* CLOCK_REALTIME
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*/
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bl V_LOCAL_FUNC(__do_get_xsec) /* get xsec from tb & kernel */
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lis r7,15 /* r7 = 1000000 = USEC_PER_SEC */
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ori r7,r7,16960
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rldicl r5,r4,44,20 /* r5 = sec = xsec / XSEC_PER_SEC */
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rldicr r6,r5,20,43 /* r6 = sec * XSEC_PER_SEC */
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std r5,TSPC64_TV_SEC(r11) /* store sec in tv */
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subf r0,r6,r4 /* r0 = xsec = (xsec - r6) */
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mulld r0,r0,r7 /* usec = (xsec * USEC_PER_SEC) /
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* XSEC_PER_SEC
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*/
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rldicl r0,r0,44,20
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mulli r0,r0,1000 /* nsec = usec * 1000 */
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std r0,TSPC64_TV_NSEC(r11) /* store nsec in tp */
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mtlr r12
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crclr cr0*4+so
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li r3,0
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blr
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50: bl V_LOCAL_FUNC(__do_get_tspec) /* get time from tb & kernel */
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bne cr1,80f /* if not monotonic, all done */
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/*
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* CLOCK_MONOTONIC
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*/
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50: bl V_LOCAL_FUNC(__do_get_xsec) /* get xsec from tb & kernel */
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lis r7,15 /* r7 = 1000000 = USEC_PER_SEC */
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ori r7,r7,16960
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rldicl r5,r4,44,20 /* r5 = sec = xsec / XSEC_PER_SEC */
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rldicr r6,r5,20,43 /* r6 = sec * XSEC_PER_SEC */
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subf r0,r6,r4 /* r0 = xsec = (xsec - r6) */
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mulld r0,r0,r7 /* usec = (xsec * USEC_PER_SEC) /
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* XSEC_PER_SEC
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*/
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rldicl r6,r0,44,20
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mulli r6,r6,1000 /* nsec = usec * 1000 */
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/* now we must fixup using wall to monotonic. We need to snapshot
|
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* that value and do the counter trick again. Fortunately, we still
|
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* have the counter value in r8 that was returned by __do_get_xsec.
|
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* At this point, r5,r6 contain our sec/nsec values.
|
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* can be used
|
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* have the counter value in r8 that was returned by __do_get_tspec.
|
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* At this point, r4,r5 contain our sec/nsec values.
|
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*/
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lwa r4,WTOM_CLOCK_SEC(r3)
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lwa r7,WTOM_CLOCK_NSEC(r3)
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lwa r6,WTOM_CLOCK_SEC(r3)
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lwa r9,WTOM_CLOCK_NSEC(r3)
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/* We now have our result in r4,r7. We create a fake dependency
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/* We now have our result in r6,r9. We create a fake dependency
|
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* on that result and re-check the counter
|
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*/
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or r9,r4,r7
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xor r0,r9,r9
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or r0,r6,r9
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xor r0,r0,r0
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add r3,r3,r0
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ld r0,CFG_TB_UPDATE_COUNT(r3)
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cmpld cr0,r0,r8 /* check if updated */
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bne- 50b
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|
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/* Calculate and store result. Note that this mimmics the C code,
|
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* which may cause funny results if nsec goes negative... is that
|
||||
* possible at all ?
|
||||
/* Add wall->monotonic offset and check for overflow or underflow.
|
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*/
|
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add r4,r4,r5
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||||
add r7,r7,r6
|
||||
lis r9,NSEC_PER_SEC@h
|
||||
ori r9,r9,NSEC_PER_SEC@l
|
||||
cmpl cr0,r7,r9
|
||||
cmpli cr1,r7,0
|
||||
add r4,r4,r6
|
||||
add r5,r5,r9
|
||||
cmpd cr0,r5,r7
|
||||
cmpdi cr1,r5,0
|
||||
blt 1f
|
||||
subf r7,r9,r7
|
||||
subf r5,r7,r5
|
||||
addi r4,r4,1
|
||||
1: bge cr1,1f
|
||||
1: bge cr1,80f
|
||||
addi r4,r4,-1
|
||||
add r7,r7,r9
|
||||
1: std r4,TSPC64_TV_SEC(r11)
|
||||
std r7,TSPC64_TV_NSEC(r11)
|
||||
add r5,r5,r7
|
||||
|
||||
80: std r4,TSPC64_TV_SEC(r11)
|
||||
std r5,TSPC64_TV_NSEC(r11)
|
||||
|
||||
mtlr r12
|
||||
crclr cr0*4+so
|
||||
|
|
@ -168,10 +127,6 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
|
|||
/*
|
||||
* syscall fallback
|
||||
*/
|
||||
98:
|
||||
mtlr r12
|
||||
mr r3,r10
|
||||
mr r4,r11
|
||||
99:
|
||||
li r0,__NR_clock_gettime
|
||||
sc
|
||||
|
|
@ -253,3 +208,59 @@ V_FUNCTION_BEGIN(__do_get_xsec)
|
|||
blr
|
||||
.cfi_endproc
|
||||
V_FUNCTION_END(__do_get_xsec)
|
||||
|
||||
/*
|
||||
* This is the core of clock_gettime(), it returns the current
|
||||
* time in seconds and nanoseconds in r4 and r5.
|
||||
* It expects the datapage ptr in r3 and doesn't clobber it.
|
||||
* It clobbers r0 and r6 and returns NSEC_PER_SEC in r7.
|
||||
* On return, r8 contains the counter value that can be reused.
|
||||
* This clobbers cr0 but not any other cr field.
|
||||
*/
|
||||
V_FUNCTION_BEGIN(__do_get_tspec)
|
||||
.cfi_startproc
|
||||
/* check for update count & load values */
|
||||
1: ld r8,CFG_TB_UPDATE_COUNT(r3)
|
||||
andi. r0,r8,1 /* pending update ? loop */
|
||||
bne- 1b
|
||||
xor r0,r8,r8 /* create dependency */
|
||||
add r3,r3,r0
|
||||
|
||||
/* Get TB & offset it. We use the MFTB macro which will generate
|
||||
* workaround code for Cell.
|
||||
*/
|
||||
MFTB(r7)
|
||||
ld r9,CFG_TB_ORIG_STAMP(r3)
|
||||
subf r7,r9,r7
|
||||
|
||||
/* Scale result */
|
||||
ld r5,CFG_TB_TO_XS(r3)
|
||||
sldi r7,r7,12 /* compute time since stamp_xtime */
|
||||
mulhdu r6,r7,r5 /* in units of 2^-32 seconds */
|
||||
|
||||
/* Add stamp since epoch */
|
||||
ld r4,STAMP_XTIME+TSPC64_TV_SEC(r3)
|
||||
ld r5,STAMP_XTIME+TSPC64_TV_NSEC(r3)
|
||||
or r0,r4,r5
|
||||
or r0,r0,r6
|
||||
xor r0,r0,r0
|
||||
add r3,r3,r0
|
||||
ld r0,CFG_TB_UPDATE_COUNT(r3)
|
||||
cmpld r0,r8 /* check if updated */
|
||||
bne- 1b /* reload if so */
|
||||
|
||||
/* convert to seconds & nanoseconds and add to stamp */
|
||||
lis r7,NSEC_PER_SEC@h
|
||||
ori r7,r7,NSEC_PER_SEC@l
|
||||
mulhwu r0,r6,r7 /* compute nanoseconds and */
|
||||
srdi r6,r6,32 /* seconds since stamp_xtime */
|
||||
clrldi r0,r0,32
|
||||
add r5,r5,r0 /* add nanoseconds together */
|
||||
cmpd r5,r7 /* overflow? */
|
||||
add r4,r4,r6
|
||||
bltlr /* all done if no overflow */
|
||||
subf r5,r7,r5 /* if overflow, adjust */
|
||||
addi r4,r4,1
|
||||
blr
|
||||
.cfi_endproc
|
||||
V_FUNCTION_END(__do_get_tspec)
|
||||
|
|
|
|||
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