munmap ends up calling tlb_flush() which for ARC was flushing the entire
TLB unconditionally (by moving the MMU to a new ASID)
do_munmap
unmap_region
unmap_vmas
unmap_single_vma
unmap_page_range
tlb_start_vma
zap_pud_range
tlb_end_vma()
tlb_finish_mmu
tlb_flush() ---> unconditional flush_tlb_mm()
So even a single page munmap, a frequent operation when uClibc dynamic
linker (ldso) is loading the dependent shared libraries, would move the
the ASID multiple times - needlessly invalidating the pre-faulted TLB
entries (and increasing the rate of ASID wraparound + full TLB flush).
This is now optimised to only be called if tlb->full_mm (which means
for exit/execve) cases only. And for those cases, flush_tlb_mm() is
already optimised to be a no-op for mm->mm_users == 0.
So essentially there are no mmore full mm flushes - except for fork which
anyhow needs it for properly COW'ing parent address space.
munmap now needs to do TLB range flush, which is implemented with
tlb_end_vma()
Results
-------
1. ASID now consistenly moves by 4 during a simple ls (as opposed to 5 or
7 before).
2. LMBench microbenchmark also shows improvements
Basic system parameters
------------------------------------------------------------------------------
Host OS Description Mhz tlb cache mem scal
pages line par load
bytes
--------- ------------- ----------------------- ---- ----- ----- ------ ----
3.9-rc5-0 Linux 3.9.0-r 3.9-rc5-0404-gcc-4.4-ba 80 8 64 1.1000 1
3.9-rc5-0 Linux 3.9.0-r 3.9-rc5-0405-avoid-full 80 8 64 1.1200 1
Processor, Processes - times in microseconds - smaller is better
------------------------------------------------------------------------------
Host OS Mhz null null open slct sig sig fork exec sh
call I/O stat clos TCP inst hndl proc proc proc
--------- ------------- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ----
3.9-rc5-0 Linux 3.9.0-r 80 4.81 8.69 68.6 118. 239. 8.53 31.6 4839 13.K 34.K
3.9-rc5-0 Linux 3.9.0-r 80 4.46 8.36 53.8 91.3 223. 8.12 24.2 4725 13.K 33.K
File & VM system latencies in microseconds - smaller is better
-------------------------------------------------------------------------------
Host OS 0K File 10K File Mmap Prot Page 100fd
Create Delete Create Delete Latency Fault Fault selct
--------- ------------- ------ ------ ------ ------ ------- ----- ------- -----
3.9-rc5-0 Linux 3.9.0-r 314.7 223.2 1054.9 390.2 3615.0 1.590 20.1 126.6
3.9-rc5-0 Linux 3.9.0-r 265.8 183.8 1014.2 314.1 3193.0 6.910 18.8 110.4
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
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