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