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[SPARC64]: Implement atomic backoff.

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When the cpu count is high and contention hits an atomic object, the
processors can synchronize such that some cpus continually get knocked
out and cannot complete the atomic update.

So implement an exponential backoff when SMP.

Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
David S. Miller 2007-10-15 16:41:44 -07:00
commit 24f287e412
3 changed files with 76 additions and 20 deletions
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28
include/asm-sparc64/backoff.h Normal file
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#ifndef _SPARC64_BACKOFF_H
#define _SPARC64_BACKOFF_H
#define BACKOFF_LIMIT (4 * 1024)
#ifdef CONFIG_SMP
#define BACKOFF_SETUP(reg) \
mov 1, reg
#define BACKOFF_SPIN(reg, tmp, label) \
mov reg, tmp; \
88: brnz,pt tmp, 88b; \
sub tmp, 1, tmp; \
cmp reg, BACKOFF_LIMIT; \
bg,pn %xcc, label; \
nop; \
ba,pt %xcc, label; \
sllx reg, 1, reg;
#else
#define BACKOFF_SETUP(reg)
#define BACKOFF_SPIN(reg, tmp, label)
#endif
#endif /* _SPARC64_BACKOFF_H */