linux-kernel - Re: [PATCH] perf/x86/pmu-events: Use CPU_CLK_UNHALTED.THREAD in Kernel

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Message-ID: <20200331193310.GO9917@kernel.org>
Date:   Tue, 31 Mar 2020 16:33:10 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Jin Yao <yao.jin@...ux.intel.com>, jolsa@...nel.org,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH] perf/x86/pmu-events: Use CPU_CLK_UNHALTED.THREAD in
 Kernel_Utilization metric

Em Tue, Mar 31, 2020 at 03:30:25PM -0400, Liang, Kan escreveu:
> 
> 
> On 3/8/2020 9:31 PM, Jin Yao wrote:
> > The kernel utilization metric does multiplexing currently and is somewhat
> > unreliable. The problem is that it uses two instances of the fixed counter,
> > and the kernel has to multipleplex which causes errors. So should use
> > CPU_CLK_UNHALTED.THREAD instead.
> > 
> > Before:
> > 
> >    # perf stat -M Kernel_Utilization -- sleep 1
> > 
> >    Performance counter stats for 'sleep 1':
> > 
> >            1,419,425      cpu_clk_unhalted.ref_tsc:k
> >        <not counted>      cpu_clk_unhalted.ref_tsc	(0.00%)
> > 
> > After:
> > 
> >    # perf stat -M Kernel_Utilization -- sleep 1
> > 
> >    Performance counter stats for 'sleep 1':
> > 
> >              746,688      cpu_clk_unhalted.thread:k #      0.7 Kernel_Utilization
> >            1,088,348      cpu_clk_unhalted.thread
> > 
> > Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
> 
> 
> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks, applied.

- Arnaldo