linux-kernel - Re: [PATCH] sched/fair: optimize should_we

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Message-ID: <da676f991cd2818bcb234ac4e70c3e56c5407167.camel@linux.intel.com>
Date:   Wed, 06 Sep 2023 08:56:55 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
Cc:     dietmar.eggemann@....com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
        mgorman@...hsingularity.net, mingo@...nel.org, yu.c.chen@...el.com,
        ricardo.neri-calderon@...ux.intel.com, iamjoonsoo.kim@....com,
        juri.lelli@...hat.com, rocking@...ux.alibaba.com,
        joshdon@...gle.com, mingo@...hat.com, peterz@...radead.org,
        vincent.guittot@...aro.org
Subject: Re: [PATCH] sched/fair: optimize should_we_balance for higher SMT
 systems

On Wed, 2023-09-06 at 07:36 +0530, Shrikanth Hegde wrote:
> 
> Hi Tim,
> 
> Thanks for taking a look at this patch.
> 
> > Wonder if we can avoid allocating the 
> > should_we_balance_tmpmask for SMT2 case to save memory
> > for system with large number of cores.
> > 
> > The new mask and logic I think is only needed for more than 2 threads in a core.
> 
> Code would have to be refactored quite a bit if one needs to take
> different approach for specific SMT setting. 
> 
> I think there would some cases in SMT2 that will benefit as well. 
> Lets say 1 cpu in each core is busy. the busy CPU happens to be second 
> CPU in the core. In that case, this approach would skip that instead of 
> checking if that is idle or not. 
> 
> 
That's true. This change could skip the sibling for SMT2.

Tim