Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 20 Apr 2023 21:56:11 +0200
From:   Andrea Righi <andrea.righi@canonical.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     torvalds@linux-foundation.org, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, ast@kernel.org,
        daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org,
        joshdon@google.com, brho@google.com, pjt@google.com,
        derkling@google.com, haoluo@google.com, dvernet@meta.com,
        dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com,
        linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
        kernel-team@meta.com
Subject: Re: [PATCH 28/32] sched_ext: Implement core-sched support
Message-ID: <ZEGY28sZgvEL7ssi@righiandr-XPS-13-7390>
References: <20230317213333.2174969-1-tj@kernel.org>
 <20230317213333.2174969-29-tj@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230317213333.2174969-29-tj@kernel.org>
Precedence: bulk

On Fri, Mar 17, 2023 at 11:33:29AM -1000, Tejun Heo wrote:
...
>  
> +static int balance_scx(struct rq *rq, struct task_struct *prev,
> +		       struct rq_flags *rf)
> +{
> +	int ret;
> +
> +	ret = balance_one(rq, prev, rf, true);
> +
> +	/*
> +	 * When core-sched is enabled, this ops.balance() call will be followed
> +	 * by put_prev_scx() and pick_task_scx() on this CPU and pick_task_scx()
> +	 * on the SMT siblings. Balance the siblings too.
> +	 */
> +	if (sched_core_enabled(rq)) {
> +		const struct cpumask *smt_mask = cpu_smt_mask(cpu_of(rq));

balance_scx() should be a no-op if CONFIG_SCHED_SMT is undefined or we
may get a build error here.

For example with a minimal ppc64le config (and CONFIG_SCHED_SMT off) I
can reproduce this:

 ./arch/powerpc/include/asm/smp.h:139:22: error: implicit declaration of function 'cpu_smt_mask'; did you mean 'cpu_cpu_mask'? [-Werror=implicit-function-declaration]

So maybe have something like this (or similar):

#ifdef CONFIG_SCHED_SMT
...
#else
static inline int balance_scx(struct rq *rq, struct task_struct *prev,
		       struct rq_flags *rf)
{
	return 0
}
#endif

Thanks,
-Andrea