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53 строки
2.2 KiB
Plaintext
53 строки
2.2 KiB
Plaintext
/*
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* @(#)alpha.gcc 10.1 (Sleepycat) 4/12/97
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*
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* The code appearing below is taken from Richard L. Sites, ed. "Alpha
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* Architecture Reference Manual", Digital Press, 1992, page 5-7 and 5-8.
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* There are 2 modifications:
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*
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* 1. The jump from blbs __r1,30f to !__r1, which is dictated by the way the
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* TSL_SET macro is used. The code suggested in Sites includes the main loop
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* of the spin lock, whereas in this code the rest the loop is specified in C.
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* The generated code might be suboptimal if the compiler generates a forward
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* branch for the usual case in which the mutex is uncontested.
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*
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* 2. At label 20, Sites suggests including code for testing for an excessive
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* number of _processor_ lock conflicts. (The seq_c instruction stores its
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* first argument provided that no other processor has written to a byte range
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* including its memory-location argument.) Absent such checking the code
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* below could conceivably stall silently on a multiprocessor alpha, depending
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* on how often processor/processor conflicts occur in a particular byte range.
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*
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* Note that the mb ("memory-barrier") instruction in TSL_UNSET is critical to
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* correct operation in a multiprocessor alpha (as is, of course, the mb in
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* the TSL_SET macro). Without the mb, changes to shared memory that occurred
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* inside the critical section (before the TSL_UNSET) might reach shared memory
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* _after_ the change of tsl to 0, thereby permitting another processor to see
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* an inconsistent view of the data protected by the mutex.
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*
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* For gcc/alpha, 0 is clear, 1 is set.
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*/
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#define TSL_SET(tsl) ({ \
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register tsl_t *__l = (tsl); \
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register tsl_t __r1, __r2; \
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__asm__ volatile(" \n\
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10: ldq_l %0,(%2) \n\
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blbs %0,30f \n\
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or %0,1,%1 \n\
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stq_c %1,(%2) \n\
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beq %1,20f \n\
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mb \n\
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br 30f \n\
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20: br 10b \n\
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30: " \
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: "=&r" (__r1), "=&r" (__r2) \
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: "r" (__l)); \
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!__r1; \
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})
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#define TSL_UNSET(tsl) ({ \
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register tsl_t *__l = (tsl); \
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__asm__ volatile("mb; stq $31,(%0);" : : "r" (__l)); \
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})
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#define TSL_INIT(tsl) TSL_UNSET(tsl)
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