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Date:   Mon, 17 Jul 2023 15:37:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Cc:     Tim Chen <tim.c.chen@linux.intel.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Ricardo Neri <ricardo.neri@intel.com>,
        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Valentin Schneider <vschneid@redhat.com>,
        Ionela Voinescu <ionela.voinescu@arm.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        naveen.n.rao@linux.vnet.ibm.com,
        Yicong Yang <yangyicong@hisilicon.com>,
        Barry Song <v-songbaohua@oppo.com>,
        Chen Yu <yu.c.chen@intel.com>, Hillf Danton <hdanton@sina.com>
Subject: Re: [Patch v3 1/6] sched/fair: Determine active load balance for SMT
 sched groups
Message-ID: <20230717133718.GJ4253@hirez.programming.kicks-ass.net>
References: <cover.1688770494.git.tim.c.chen@linux.intel.com>
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 <05ed4537-e79b-0ff3-5be5-92cbffaab3ee@linux.vnet.ibm.com>
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On Mon, Jul 17, 2023 at 05:48:02PM +0530, Shrikanth Hegde wrote:

> Hi Peter. 
> 
> Sending on behalf of tim. I have included my suggestion as well. Hope
> that's ok.  Please find below the patch as of now. it includes the
> couple of changes that are discussed. (in 1/6 and in 3/6)

Could you please add a Changelog and SoB thingies such that I can apply
the thing?

Given Tim is on holidays, perhaps do something like:

Originally-by: Tim Chen <...>

After all, you did some changes and verified it actually works etc..


> ---
>  kernel/sched/fair.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 932e7b78894a..9502013abe33 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9532,7 +9532,7 @@ static inline long sibling_imbalance(struct lb_env *env,
>  	imbalance /= ncores_local + ncores_busiest;
>  
>  	/* Take advantage of resource in an empty sched group */
> -	if (imbalance == 0 && local->sum_nr_running == 0 &&
> +	if (imbalance <= 1 && local->sum_nr_running == 0 &&
>  	    busiest->sum_nr_running > 1)
>  		imbalance = 2;
>  
> @@ -9720,6 +9720,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
>  		break;
>  
>  	case group_smt_balance:
> +		/* no idle cpus on both groups handled by group_fully_busy below */
> +		if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
> +			if (sgs->idle_cpus > busiest->idle_cpus)
> +				return false;
> +			if (sgs->idle_cpus < busiest->idle_cpus)
> +				return true;
> +			if (sgs->sum_nr_running <= busiest->sum_nr_running)
> +				return false;
> +		}
> +		break;
> +
>  	case group_fully_busy:
>  		/*
>  		 * Select the fully busy group with highest avg_load. In
> -- 
> 2.31.1