linux-kernel - Re: [PATCH] intel_idle: Add Jasper Lake and Elkhart Lake support

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Message-ID: <CAAd53p52A7ymkQhFweoy2vRXfkT81pumU6V5Q8tbEBKTnX=ASg@mail.gmail.com>
Date: Thu, 1 Aug 2024 14:54:50 +0800
From: Kai-Heng Feng <kai.heng.feng@...onical.com>
To: Len Brown <lenb@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, "Zhang, Rui" <rui.zhang@...el.com>, 
	"jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>, 
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
	"artem.bityutskiy@...ux.intel.com" <artem.bityutskiy@...ux.intel.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH] intel_idle: Add Jasper Lake and Elkhart Lake support

On Thu, Aug 1, 2024 at 12:28 AM Len Brown <lenb@...nel.org> wrote:
>
> On Wed, Jul 31, 2024 at 2:18 AM Kai-Heng Feng
> <kai.heng.feng@...onical.com> wrote:
> >
> > The crucial part to make the issue (i.e. slow ethernet) is
> > ".disable_promotion_to_c1e = true".
>
> Okay, so the problem statement is that on this machine with some
> ethernet controller and some workload,
> performance is better when you use just C1 and not C1E (or deeper) states.
>
> And so you want to have the option of accessing C1 without the overhead of C1E?

Yes, that's the case here.

>
> Presumably you don't care about the power savings of the deeper states,
> or you are using PM_QOS to avoid deep c-states at run time?

I tried to use cpu_latency_qos in the network driver's NAPI poll, but
only saw marginal improvement to around 830Mbps. Hitting the 940Mbps
is still the goal here.

>
> > Can we use that for EHL and JSL?
>
> Yes.

Is it plausible to disable C1E promotion while using ACPI idle driver?
Or provide a C-state table in intel_idle and update the states via
_CST?

>
> You may also have a BIOS option to achieve the same goal, depending on
> the platform.)

I am seeing three different platforms from different vendors hitting
the same issue, so it's better to disable C1e for these platforms.

Kai-Heng

>
> --
> Len Brown, Intel
>