John Baldwin writes: > and lfence is only on PIV+. I don't recall when mfence first appeared.. > perhaps PII? If the lock is really expensive, then perhaps we could make > atomic_cmpset() be actual functions (ugh) rather than inlines that did a > branch to use foofence for PIV rather than the default. The branches would > suck, but it might be faster than the lock. Of course, this would greatly > pessimize non-PIV. According to http://www.sandpile.org/ia32/coherent.htm, both mfence and lfence require SSE2, so sfence has the broadest coverage. But since only P4 needs it, and since lfence is ~25% cheaper, maybe there should be a separate config option for it, and it should be a straight conditional compile option for those of us cursed w/P4s. DrewReceived on Thu May 06 2004 - 09:26:26 UTC
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