Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
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- Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
- From: Ingo Molnar <mingo@xxxxxxx>
- Date: Mon, 15 Jun 2009 20:28:28 +0200
- Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, mingo@xxxxxxxxxx, hpa@xxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, a.p.zijlstra@xxxxxxxxx, penberg@xxxxxxxxxxxxxx, vegard.nossum@xxxxxxxxx, efault@xxxxxx, jeremy@xxxxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <20090615182348.GC11248@xxxxxxx>
- References: <tip-74193ef0ecab92535c8517f082f1f50504526c9b@xxxxxxxxxxxxxx> <alpine.LFD.2.01.0906151007560.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615171845.GA7664@xxxxxxx> <alpine.LFD.2.01.0906151029160.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615180527.GB4201@Krystal> <20090615182348.GC11248@xxxxxxx>
- User-agent: Mutt/1.5.18 (2008-05-17)
* Ingo Molnar <mingo@xxxxxxx> wrote:
> The GUP based method is pretty generic though - and can be used on
> other architectures as well. It's not as fast as direct access
> though.
Another question is: your patch switches over all normal exceptions
from IRET to hand-unroll+RET.
It would be really nice to benchmark it (via 'perf stat' for example
;-) whether that's a slowdown or a speedup.
If it's a slowdown then the decision is easy: we dont want this, we
want to push the overhead into the sampling code, away from common
codepaths.
[ If on the other hand it's a speedup of a few cycles then we have
the problem of me suddenly liking this patch a whole lot more ;-) ]
Ingo
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