linux-kernel - Re: [PATCH] intel_idle: add CPUIDLE_FLAG_IRQ

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Date:   Fri, 1 Jul 2022 14:06:50 +0000
From:   Jon Kohler <jon@...anix.com>
To:     Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
CC:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] intel_idle: add CPUIDLE_FLAG_IRQ_ENABLE to SPR C1 and C1E



> On Jul 1, 2022, at 9:30 AM, Artem Bityutskiy <artem.bityutskiy@...ux.intel.com> wrote:
> 
> Hi Jon,
> 
> On Thu, 2022-06-30 at 15:43 -0400, Jon Kohler wrote:
>> Add CPUIDLE_FLAG_IRQ_ENABLE to spr_cstates C1 and C1E, which will
>> allow local IRQs to be enabled during fast idle transitions on SPR.
> 
> Did you have a chance to measure this? When I was doing this for ICX and CLX, I
> was using cyclictest and wult for measuring IRQ latency.
> 
> I was planning to do this for SPR as well.

We have the ‘before’ baseline from wult, and realized after doing it that
IRQ_ENABLE config wasn’t set. I’ve provided this patch to our internal
team working on SPR enablement to get another wult run in next week.

That said, if you’ve got access to an SPR system setup as well, we’d
certainly appreciate a second set of eyes. This is the first generation
of enablement for a new platform that we’ve done where wult has been
on the ‘checklist’ so to speak, so we don’t have as much ’stick time’
on it as someone like yourself would :) 

> 
>> Note: Enabling this for both C1 and C1E is slightly different than
>> the approach for SKX/ICX, where CPUIDLE_FLAG_IRQ_ENABLE is only
>> enabled on C1; however, given that SPR target/exit latency is 1/1
>> for c1 and 2/4 for C1E, respectively, which is slower than C1
>> for SKX, it seems prudent to now enable it on both states.
> 
> I was also going to measure this for C1E.
> 
> Could we please hold on this a bit - I'd like to measure this before we merge
> it.

Yea no problem, happy to get help and a second set of eyes on this.

Thanks - Jon

> 
> Artem.
>