linux-kernel - Re: [PATCH v2 0/2] sched: blk: Handle HMP systems when completing IO

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Date: Sat, 24 Feb 2024 19:13:24 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Qais Yousef <qyousef@...alina.io>
Cc: linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Sudeep Holla <sudeep.holla@....com>, Wei Wang <wvw@...gle.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Bart Van Assche <bvanassche@....org>,
        Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>,
        Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v2 0/2] sched: blk: Handle HMP systems when completing IO



On 2/23/24 9:27 PM, Qais Yousef wrote:
> Due to recent changes in how topology is represented on asymmetric multi
> processing systems like big.LITTLE where all cpus share the last LLC, there is
> a performance regression as cpus with different compute capacities appear under
> the same LLC and we no longer send an IPI when the requester is running on
> a different cluster with different compute capacity.
> 
> Restore the old behavior by adding a new cpus_equal_capacity() function to help
> check for the new condition for these systems.
> 
> Changes since v1:
> 
> 	* Split the patch per subsystem.
> 	* Convert cpus_gte_capacity() to cpus_equal_capacity()
> 	* Make cpus_equal_capacity() return immediately for SMP systems.
> 

nit: Did you mean !SMP systems here? 
Because in changes i see its returning true directly if its in !CONFIG_SMP path. 

> Qais Yousef (2):
>   sched: Add a new function to compare if two cpus have the same
>     capacity
>   block/blk-mq: Don't complete locally if capacities are different
> 
>  block/blk-mq.c                 |  5 +++--
>  include/linux/sched/topology.h |  6 ++++++
>  kernel/sched/core.c            | 11 +++++++++++
>  3 files changed, 20 insertions(+), 2 deletions(-)
>