linux-kernel - Re: [PATCHv2 2/2] trace/hwlat: Do not start per-cpu thread if it is already running

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Date:   Fri, 10 Mar 2023 14:52:34 +0100
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Tero Kristo <tero.kristo@...ux.intel.com>, rostedt@...dmis.org,
        mhiramat@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv2 2/2] trace/hwlat: Do not start per-cpu thread if it is
 already running

On 3/10/23 11:04, Tero Kristo wrote:
> The hwlatd tracer will end up starting multiple per-cpu threads with
> the following script:
> 
>     #!/bin/sh
>     cd /sys/kernel/debug/tracing
>     echo 0 > tracing_on
>     echo hwlat > current_tracer
>     echo per-cpu > hwlat_detector/mode
>     echo 100000 > hwlat_detector/width
>     echo 200000 > hwlat_detector/window
>     echo 1 > tracing_on
> 
> To fix the issue, check if the hwlatd thread for the cpu is already
> running, before starting a new one. Along with the previous patch, this
> avoids running multiple instances of the same CPU thread on the system.
> 
> Signed-off-by: Tero Kristo <tero.kristo@...ux.intel.com>

Acked-by: Daniel Bristot de Oliveira <bristot@...nel.org>

-- Daniel