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

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Message-ID: <b35cf10b03b441a95704648e816ff1acc150f38b.camel@linux.intel.com>
Date:   Fri, 01 Jul 2022 16:30:07 +0300
From:   Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
To:     Jon Kohler <jon@...anix.com>,
        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-kernel@...r.kernel.org
Subject: Re: [PATCH] intel_idle: add CPUIDLE_FLAG_IRQ_ENABLE to SPR C1 and
 C1E

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.

> 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.

Artem.