linux-kernel - Re: [PATCH v2 0/2] intel_powerclamp: New module parameter

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Date:   Tue, 7 Feb 2023 05:42:37 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Zhang, Rui" <rui.zhang@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 0/2] intel_powerclamp: New module parameter

On Mon, Feb 06, 2023 at 02:02:28AM -0800, srinivas pandruvada wrote:
> On Mon, 2023-02-06 at 08:05 +0000, Zhang, Rui wrote:
> > On Sun, 2023-02-05 at 18:45 -0800, srinivas pandruvada wrote:
> > > Hi Rui,
> > > 
> > > On Sun, 2023-02-05 at 15:57 +0000, Zhang, Rui wrote:
> > > > Hi, Srinivas,
> > > > 
> > > > First of all, the previous build error is gone.
> > > > 
> > > > Second, I found something strange, which may be related with the
> > > > scheduler asym-packing, so CC Ricardo.
> > > > 
> > > I thought you disable ITMT before idle injection and reenebale
> > > after
> > > removal.
> > 
> > No.
> > 
> > I can reproduce this by playing with raw intel_powerclamp sysfs knobs
> > and ITMT enabled.
> > 
> 
> This issue is happening even if ITMT disabled. If the module mask is
> composed of P-cores it works or even on servers as expected.
> Also if you offline all P-cores then select mask among E-cores, it is
> working. Somehow P-core influences E-cores.
> 
> Since this patch is module mask related, that is functioning correctly.
> We have to debug this interaction with P and E cores separately.

Currently, when doing asym_packing, ECores will only pull tasks from a
PCore only if both SMT siblings are busy. It will only pull from the
lower-priority sibling. These patches [1] let ECores pull from either
sibling, if both are busy.

I presume that by injecting idle, the scheduler thinks that the CPU is
idle (i.e., idle_cpu() returns true) and it will not do asym_packing from
lower-priority CPUs.

However, in your experiment you have 16 threads. If a Pcore is overloaded,
an ECore should be able to help.

[1]. https://lore.kernel.org/lkml/20230207045838.11243-1-ricardo.neri-calderon@linux.intel.com/