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Date:   Fri, 5 May 2023 15:23:47 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Tim Chen <tim.c.chen@linux.intel.com>
Cc:     Ricardo Neri <ricardo.neri-calderon@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,
        Shrikanth Hegde <sshegde@linux.vnet.ibm.com>,
        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>
Subject: Re: [PATCH 5/6] sched/fair: Consider the idle state of the whole
 core for load balance
Message-ID: <20230505132347.GR83892@hirez.programming.kicks-ass.net>
References: <cover.1683156492.git.tim.c.chen@linux.intel.com>
 <849d3fee51d218de71ecc9d557667ff6b137ac2d.1683156492.git.tim.c.chen@linux.intel.com>
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On Thu, May 04, 2023 at 09:09:55AM -0700, Tim Chen wrote:

> @@ -10709,11 +10709,26 @@ static int should_we_balance(struct lb_env *env)
>  	for_each_cpu_and(cpu, group_balance_mask(sg), env->cpus) {
>  		if (!idle_cpu(cpu))
>  			continue;
> +		else {
> +			/*
> +			 * Don't balance to idle SMT in busy core right away when
> +			 * balancing cores, but remember the first idle SMT CPU for
> +			 * later consideration.  Find CPU on an idle core first.
> +			 */
> +			if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && !is_core_idle(cpu)) {
> +				if (idle_smt == -1)
> +					idle_smt = cpu;
> +				continue;
> +			}
> +		}

Not only does that bust CodingStyle, it's also entirely daft. What
exactly is the purpose of that else statement?

>  
>  		/* Are we the first idle CPU? */
>  		return cpu == env->dst_cpu;
>  	}