linux-kernel - Re: [PATCH 0/2] measure latency of cpu hotplug path

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Date:   Thu, 24 Sep 2020 10:58:23 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     peterz@...radead.org
Cc:     Prasad Sodagudi <psodagud@...eaurora.org>, tglx@...utronix.de,
        qais.yousef@....com, mingo@...nel.org, cai@....pw,
        tyhicks@...onical.com, arnd@...db.de, rameezmustafa@...eaurora.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] measure latency of cpu hotplug path

On Thu, 24 Sep 2020 10:34:14 +0200
peterz@...radead.org wrote:

> On Wed, Sep 23, 2020 at 04:37:44PM -0700, Prasad Sodagudi wrote:
> > There are all changes related to cpu hotplug path and would like to seek
> > upstream review. These are all patches in Qualcomm downstream kernel
> > for a quite long time. First patch sets the rt prioity to hotplug
> > task and second patch adds cpuhp trace events.
> > 
> > 1) cpu-hotplug: Always use real time scheduling when hotplugging a CPU
> > 2) cpu/hotplug: Add cpuhp_latency trace event  
> 
> Why? Hotplug is a known super slow path. If you care about hotplug
> latency you're doing it wrong.

I'd like to know the answer to Peter's question too. Why?

-- Steve