linux-kernel - Re: [PATCH v2 2/3] sched/fair: Ignore isolated cpus in update_numa

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Message-ID: <7941d5e5-e96a-4356-b5e7-8e61f89d2748@linux.ibm.com>
Date: Wed, 8 Jan 2025 00:00:16 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Chuyi Zhou <zhouchuyi@...edance.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        vschneid@...hat.com, longman@...hat.com, riel@...riel.com,
        chengming.zhou@...ux.dev, kprateek.nayak@....com,
        linux-kernel@...r.kernel.org,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH v2 2/3] sched/fair: Ignore isolated cpus in
 update_numa_stat

On 07/01/25 18:46, Chuyi Zhou wrote:
> Hello Madadi Vineeth Reddy,
> 
> 在 2025/1/6 02:52, Madadi Vineeth Reddy 写道:
>> On 03/01/25 12:29, Chuyi Zhou wrote:
>>> Now update_numa_stats() iterates each cpu in a node to gather load
>>> information for the node and attempts to find the idle cpu as a candidate
>>> best_cpu within the node.
>>>
>>> In update_numa_stats() we should take into account the scheduling domain.
>>> This is because the "isolcpus" kernel command line option and cpuset iso-
>>> late partitions can remove CPUs from load balance. Similar to task wakeup
>>> and periodic load balancing, we should not involve isolated CPUs in NUMA
>>> balancing. When gathering load information for nodes, we need to ignore the
>>> load of isolated CPUs. This change also avoids selecting an isolated CPU
>>> as the idle_cpu.
>>
>> If possible, would you be able to share any performance metrics or benchmarks
>> that demonstrate the impact of this patch on NUMA balancing or CPU migration
>> efficiency?
>>
>> Thanks,
>> Madadi Vineeth Reddy
>>
> 
> This change will not alter the default behavior of NUMA balancing unless we enables both NUMA balancing and isolated CPUs features. Therefore, under normal default conditions, there should be no performance regression. On the other hand, involving isolated CPUs in NUMA balancing or load balancing is inappropriate, and this is the issue that this patch aims to fix.
> 
> It might be worth setting up a test scenario for cases where NUMA balancing and isolated CPUs are both enabled. Perhaps this testing will be done later on.

Right, by benchmark, I meant the scenario where both NUMA balancing and isolated
CPUs are involved. It would make for an interesting test case.

Thanks,
Madadi Vineeth Reddy

> 
> Thanks.