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

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Message-ID: <CAJZ5v0i9Qt3OFKCbqkd-q4VKYreV2PZZpQ2Km9az2htANG5zxA@mail.gmail.com>
Date: Tue, 30 Jul 2024 15:59:43 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc: "Zhang, Rui" <rui.zhang@...el.com>, 
	"jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>, "lenb@...nel.org" <lenb@...nel.org>, 
	"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>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH] intel_idle: Add Jasper Lake and Elkhart Lake support

On Mon, Jul 29, 2024 at 6:08 AM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> [+Cc Rafael, Srinivas]
>
> On Fri, Jul 26, 2024 at 2:52 PM Zhang, Rui <rui.zhang@...el.com> wrote:
> >
> > On Fri, 2024-07-26 at 14:26 +0800, Kai-Heng Feng wrote:
> > > Without proper C-state support, the CPU can take long time to exit to
> > > C0
> > > to handle IRQ and perform DMA.
> >
> > Can you provide more details?
> >
> > Say, what cstate is entered w/ and w/o this patch?
>
> Without the patch it's ACPI C1, C2 and C3.

They are called like this because they come from ACPI _CST.  You need
to use turbostat (or equivalent) to check what C-states really are
entered.

>
> >
> > can you show the output of "grep .
> > /sys/devices/system/cpu/cpu0/cpuidle/state*/*" without this patch?
>
> /sys/devices/system/cpu/cpu0/cpuidle$ grep . */*
> state0/above:0
> state0/below:631
> state0/default_status:enabled
> state0/desc:CPUIDLE CORE POLL IDLE
> state0/disable:0
> state0/latency:0
> state0/name:POLL
> state0/power:4294967295
> state0/rejected:0
> state0/residency:0
> state0/time:19513
> state0/usage:635
> state1/above:26
> state1/below:12437
> state1/default_status:enabled
> state1/desc:ACPI FFH MWAIT 0x0

This is C1 AFAICS.

> state1/disable:0
> state1/latency:1
> state1/name:C1_ACPI
> state1/power:0
> state1/rejected:0
> state1/residency:1
> grep: state1/s2idle: Is a directory
> state1/time:18621370
> state1/usage:74523
> state2/above:1690
> state2/below:17
> state2/default_status:enabled
> state2/desc:ACPI FFH MWAIT 0x31

This looks like something that used to be called "C7s".

> state2/disable:0
> state2/latency:253
> state2/name:C2_ACPI
> state2/power:0
> state2/rejected:0
> state2/residency:759
> grep: state2/s2idle: Is a directory
> state2/time:7063052
> state2/usage:7909
> state3/above:13111
> state3/below:0
> state3/default_status:enabled
> state3/desc:ACPI FFH MWAIT 0x60

And this looks like C10.

> state3/disable:0
> state3/latency:1048
> state3/name:C3_ACPI
> state3/power:0
> state3/rejected:0
> state3/residency:3144
> grep: state3/s2idle: Is a directory
> state3/time:4451519230
> state3/usage:55467
>
>
> >
> > >
> > > The data collect via wult shows the latency is similar to Broxton, so
> > > use the existing table to support C-state on JSL and EHL.
> >
> > so you have done cstate measurement on the EHL using wult?
> > can you share more details about the measurement results?
>
> I look at the "spikes" of the aggregated graph. Not sure if it's the
> right way to interpret the graph though.
>
> It will be much better if Intel can add the proper C-states table for
> JSL and EHL.

So what's missing in the above, from the technical standpoint?