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: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
- Date: Mon, 15 Jun 2009 21:10:11 +0200
- Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, mingo@xxxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, penberg@xxxxxxxxxxxxxx, vegard.nossum@xxxxxxxxx, efault@xxxxxx, jeremy@xxxxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <20090615190759.GA12778@xxxxxxx>
- References: <tip-74193ef0ecab92535c8517f082f1f50504526c9b@xxxxxxxxxxxxxx> <alpine.LFD.2.01.0906151007560.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615171845.GA7664@xxxxxxx> <alpine.LFD.2.01.0906151029160.3305@xxxxxxxxxxxxxxxxxxxxx> <4A369508.2090707@xxxxxxxxx> <20090615184858.GD6520@Krystal> <1245091917.6741.185.camel@laptop> <20090615185907.GF6520@Krystal> <20090615190321.GA11641@xxxxxxx> <20090615190759.GA12778@xxxxxxx>
On Mon, 2009-06-15 at 21:07 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@xxxxxxx> wrote:
>
> > > To a point where it cannot afford a simple register save/restore
> > > ?
> > >
> > > There is "caring" and "_caring_". I am tempted to ask what NMI
> > > handler execution frequency you have in mind here to figure out
> > > if we are not trying to optimize sub-nanoseconds per minutes. ;)
> >
> > I routinely run 'perf' with half a million NMIs per second or
> > more. ( Why wait 10 seconds for a profile you can get in 1 second?
> > ;-)
> >
> > Granted that is over multiple CPUs - but still performance does
> > matter here too.
> >
> > Reading cr2 is certainly fast. Writing it - dunno.
>
> But one thing is sure: it is certainly going to be faster than the
> INVLPG(s!) we have to do with the GUP solution.
Sure, but we only pay that price when we do the callchain bit, not on
every NMI.
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