4.7 vs 5.2.1 SMP/UP bridging performance

[John Baldwin]

On Thursday 06 May 2004 02:26 pm, Andrew Gallatin wrote:
> 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.

That could work I guess.  Just can't stick it in GENERIC.

options	INTEL_MADE_MY_PIV_A_TORTOISE

or some such. :)

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org