Re: [PATCH 3/5] x86/mwait-idle: update ICX C6 data

From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH 3/5] x86/mwait-idle: update ICX C6 data
Date: Tue, 18 Jan 2022 15:08:29 +0100	[thread overview]
Message-ID: <65dafbcc-d627-623b-ed78-83c3bfa25e00@suse.com> (raw)
In-Reply-To: <YeaUdIHubGgtVpV2@Air-de-Roger>

On 18.01.2022 11:20, Roger Pau Monné wrote:
> On Mon, Sep 06, 2021 at 03:01:12PM +0200, Jan Beulich wrote:
>> From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
>>
>> Change IceLake Xeon C6 latency from 128 us to 170 us. The latency
>> was measured with the "wult" tool and corresponds to the 99.99th
>> percentile when measuring with the "nic" method. Note, the 128 us
>> figure correspond to the median latency, but in intel_idle we use
>> the "worst case" latency figure instead.
>>
>> C6 target residency was increased from 384 us to 600 us, which may
>> result in less C6 residency in some workloads. This value was tested
>> and compared to values 384, and 1000. Value 600 is a reasonable
>> tradeoff between power and performance.
>>
>> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
>> Acked-by: Zhang Rui <rui.zhang@intel.com>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> [Linux commit: d484b8bfc6fa71a088e4ac85d9ce11aa0385867e]
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Acked-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks.

> AFAICT those values are all from measurements, and not in any manual
> or specification?

That's my understanding of the description, yes.

Jan