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Date: Mon, 1 Apr 2024 19:00:11 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Vitalii Bursov <vitaly@...sov.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira
<bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] docs: cgroup-v1: clarify that domain levels are
system-specific
On 4/1/24 4:05 PM, Vitalii Bursov wrote:
>
>
> On 01.04.24 07:05, Shrikanth Hegde wrote:
>>
>>
>> On 3/31/24 9:31 PM, Vitalii Bursov wrote:
>>> Add a clarification that domain levels are system-specific
>>> and where to check for system details.
>>>
>>> Add CPU clusters to the scheduler domain levels table.
>>>
>>> Signed-off-by: Vitalii Bursov <vitaly@...sov.com>
>>> ---
>>> Documentation/admin-guide/cgroup-v1/cpusets.rst | 16 +++++++++++-----
>>> 1 file changed, 11 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/cgroup-v1/cpusets.rst b/Documentation/admin-guide/cgroup-v1/cpusets.rst
>>> index 7d3415eea..d16a3967d 100644
>>> --- a/Documentation/admin-guide/cgroup-v1/cpusets.rst
>>> +++ b/Documentation/admin-guide/cgroup-v1/cpusets.rst
>>> @@ -568,19 +568,25 @@ on the next tick. For some applications in special situation, waiting
>>>
>>> The 'cpuset.sched_relax_domain_level' file allows you to request changing
>>> this searching range as you like. This file takes int value which
>>> -indicates size of searching range in levels ideally as follows,
>>> +indicates size of searching range in levels approximately as follows,
>>> otherwise initial value -1 that indicates the cpuset has no request.
>>>
>>> ====== ===========================================================
>>> -1 no request. use system default or follow request of others.
>>> 0 no search.
>>> 1 search siblings (hyperthreads in a core).
>>> - 2 search cores in a package.
>>> - 3 search cpus in a node [= system wide on non-NUMA system]
>>> - 4 search nodes in a chunk of node [on NUMA system]
>>> - 5 search system wide [on NUMA system]
>>> + 2 search cpu clusters
>>> + 3 search cores in a package.
>>> + 4 search cpus in a node [= system wide on non-NUMA system]
>>> + 5 search nodes in a chunk of node [on NUMA system]
>>> + 6 search system wide [on NUMA system]
>>
>> I think above block of documentation need not change. SD_CLUSTER is a software
>> construct, not a sched domain per se.
>>
>
> I added "cpu clusters" because the original table:
> ====== ===========================================================
> -1 no request. use system default or follow request of others.
> 0 no search.
> 1 search siblings (hyperthreads in a core).
> 2 search cores in a package.
> 3 search cpus in a node [= system wide on non-NUMA system]
> 4 search nodes in a chunk of node [on NUMA system]
> 5 search system wide [on NUMA system]
> ====== ===========================================================
> does not match to what I see on a few systems I checked.
>
> AMD Ryzen and the same dual-CPU Intel server with NUMA disabled:
> level:0 - SMT
> level:2 - MC
> level:3 - PKG
>
> Server with NUMA enabled:
> level:0 - SMT
> level:2 - MC
> level:5 - NUMA
>
None of these are "cpu clusters".
>From what i know, the description for the above are.
SMT - multi-threads/hyperthreads
MC - Multi-Core
PKG - Package/Socket level
NUMA - Node level. When you enable, PKG gets degenerated since pkg mask and numa mask would
have been same.
> So, for the relax level original table:
> 1 -> enables 0 SMP -> OK
> 2 -> enables 1 unknown -> does not enable cores in a package
> 3 -> enables 2 MC -> OK for NUMA, but not system wide on non-NUMA system
> 5 -> enables 4 unknown -> does not enable system wide on NUMA
>
> The updated table
> ====== ===========================================================
> -1 no request. use system default or follow request of others.
> 0 no search.
> 1 search siblings (hyperthreads in a core).
> 2 search cpu clusters
> 3 search cores in a package.
> 4 search cpus in a node [= system wide on non-NUMA system]
> 5 search nodes in a chunk of node [on NUMA system]
> 6 search system wide [on NUMA system]
> ====== ===========================================================
> would work like this:
> 1 -> enables 0 SMP -> OK
> 2 -> enables 1 unknown -> does nothing new
> 3 -> enables 2 MC -> OK, cores in a package for NUMA and non-NUMA system
> 4 -> enables 3 PKG -> OK on non-NUMA system
It wont, PKG domain itself wont be there. It gets removed.
> 6 -> enables 5 NUMA -> OK
>
> I think it would look more correct on "average" systems, but anyway,
> please confirm and I'll remove the table update in an updated patch.
>
IMHO, the table need not get updated. Just adding a paragraph pointing
to refer to the sysfs files is good enough.
> Thanks
>
>> IMO the next paragraph that is added is good enough and the above change can be removed.
>
>>> ====== ===========================================================
>>>
>>> +Not all levels can be present and values can change depending on the
>>> +system architecture and kernel configuration. Check
>>> +/sys/kernel/debug/sched/domains/cpu*/domain*/ for system-specific
>>> +details.
>>> +
>>> The system default is architecture dependent. The system default
>>> can be changed using the relax_domain_level= boot parameter.
>>>
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