Re: cvs commit: src/sys/amd64/amd64 mp_machdep.c src/sys/i386/i386 mp_machdep.c




Am 24.04.2006 um 23:17 schrieb Colin Percival:

cperciva 2006-04-24 21:17:02 UTC

FreeBSD src repository

Modified files:
sys/amd64/amd64 mp_machdep.c
sys/i386/i386 mp_machdep.c
Log:
Adjust dangerous-shared-cache-detection logic from "all shared data
caches are dangerous" to "a shared L1 data cache is dangerous". This
is a compromise between paranoia and performance: Unlike the L1 cache,
nobody has publicly demonstrated a cryptographic side channel which
exploits the L2 cache -- this is harder due to the larger size, lower
bandwidth, and greater associativity -- and prohibiting shared L2
caches turns Intel Core Duo processors into Intel Core Solo processors.

As before, the 'machdep.hyperthreading_allowed' sysctl will allow even
the L1 data cache to be shared.

I do not pretend to understand the background, but from your description it sounds like performance on Core Duo machines will be bad unless this change is made, or the potentially dangerous sysctl is active. If that is indeed the case, will this change make it into 6.1?


Thanks,
Stefan

--
Stefan Bethke <stb@xxxxxxxxxx> Fon +49 170 346 0140


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