Re: [PATCH][3/7] perfctr-2.7.2 for 2.6.6-mm2: x86_64

From: Andi Kleen
Date: Sat May 15 2004 - 15:51:18 EST

> I want the kernel to avoid every delay that can be avoided. Do not force

There are a lot of other more frutiful targets I would focus my
attention then. e.g. you could get rid of __SLOW_DOWN_IO on modern
machines which hits all the time and is a *lot* slower than even hundreds
of pipeline flushes. Or of all the mdelays in driver code like IDE.

> a pipeline flush for speculative rdtsc. Besides those 20-30 cycles

But how useful is the "work" when it results in wrong answers?

Speculative RDTSC is not a theoretical problem, it has actually
caused problems in practice in other codes by making CPU timestamps
non monotonic.

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