linux-kernel - Re: [PATCH] sched/fair: Add SMT4 group_smt

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Message-ID: <804548a12363479d41dee19bb843002d9e105afd.camel@linux.intel.com>
Date:   Wed, 26 Jul 2023 20:11:18 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>, peterz@...radead.org
Cc:     bristot@...hat.com, bsegall@...gle.com, dietmar.eggemann@....com,
        hdanton@...a.com, ionela.voinescu@....com, juri.lelli@...hat.com,
        len.brown@...el.com, linux-kernel@...r.kernel.org, mgorman@...e.de,
        naveen.n.rao@...ux.vnet.ibm.com, rafael.j.wysocki@...el.com,
        ravi.v.shankar@...el.com, ricardo.neri@...el.com,
        rostedt@...dmis.org, srikar@...ux.vnet.ibm.com,
        srinivas.pandruvada@...ux.intel.com, v-songbaohua@...o.com,
        vincent.guittot@...aro.org, vschneid@...hat.com, x86@...nel.org,
        yangyicong@...ilicon.com, yu.c.chen@...el.com
Subject: Re: [PATCH] sched/fair: Add SMT4 group_smt_balance handling

On Mon, 2023-07-17 at 20:28 +0530, Shrikanth Hegde wrote:
> From: Tim Chen <tim.c.chen@...ux.intel.com>
> 
> For SMT4, any group with more than 2 tasks will be marked as
> group_smt_balance. Retain the behaviour of group_has_spare by marking
> the busiest group as the group which has the least number of idle_cpus.
> 
> Also, handle rounding effect of adding (ncores_local + ncores_busy)
> when the local is fully idle and busy group has more than 2 tasks.
> Local group should try to pull at least 1 task in this case.
> 
> Originally-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
> ---
>  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

Thanks for the fix up patch.

Acked-by: Tim Chen <tim.c.chen@...ux.intel.com>