linux-kernel - Re: [PATCH 0/3]measure SMI cost

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Message-ID: <alpine.DEB.2.20.1703241259540.3688@nanos>
Date:   Fri, 24 Mar 2017 13:07:42 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <ak@...ux.intel.com>
cc:     Kan Liang <kan.liang@...el.com>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, jolsa@...nel.org
Subject: Re: [PATCH 0/3]measure SMI cost

On Fri, 24 Mar 2017, Andi Kleen wrote:

> > > A new --smi-cost mode in perf stat is implemented to measure the SMI cost
> > > by calculating cycles and aperf results. In practice, the percentages of
> > > SMI cycles should be more useful than absolute value.
> > 
> > That's only true for performance oriented analysis, but for analyzing the
> > root cause of latencies the actual cycles are definitely interesting.
> 
> perf stat also prints the absolute cycles of course (unless you do --metric-only)

So much for the theory. From the patch:

+                       if (!force_metric_only)
+                               metric_only = true;

> It cannot print individual cycles (per SMI occurrence), the only
> way to do that would be to poll constantly.

I'm well aware of that.

Thanks,

	tglx