linux-kernel - Re: [PATCH] perf evlist: Fix error out while applying initial delay and LBR

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Date:   Mon, 9 Jul 2018 17:20:54 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, namhyung@...nel.org,
        ak@...ux.intel.com, sunil.k.pandey@...el.com
Subject: Re: [PATCH] perf evlist: Fix error out while applying initial delay
 and LBR

On Mon, Jul 09, 2018 at 07:15:22AM -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Perf record will error out if both --delay and LBR are applied.
> For example:
>   perf record -D 1000 -a -e cycles -j any -- sleep 2
>   Error:
>   dummy:HG: PMU Hardware doesn't support sampling/overflow-interrupts.
>   Try 'perf stat'
> 
> A dummy event is added implicitly for initial delay, which has the same
> configurations as real sampling events. The dummy event is a software
> event. If LBR is configured, perf must error out.
> 
> The dummy event only be used to track PERF_RECORD_MMAP while perf waits
> for the initial delay to enable the real events. The BRANCH_STACK bit
> can be safely cleared for the dummy event.
> 
> After applying the patch:
>   perf record -D 1000 -a -e cycles -j any -- sleep 2
>   [ perf record: Woken up 1 times to write data ]
>   [ perf record: Captured and wrote 1.054 MB perf.data (828 samples) ]
> 
> Reported-by: Pandey, Sunil K <sunil.k.pandey@...el.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka