linux-kernel - Re: [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging interface

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Message-ID: <20190426141307.GB2623@hirez.programming.kicks-ass.net>
Date:   Fri, 26 Apr 2019 16:13:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Phil Auld <pauld@...hat.com>
Cc:     Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging
 interface

On Thu, Apr 25, 2019 at 10:26:53AM -0400, Phil Auld wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e8e5f26db052..b312ea1e28a4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7541,6 +7541,9 @@ static int cpu_core_tag_write_u64(struct cgroup_subsys_state *css, struct cftype
>         if (val > 1)
>                 return -ERANGE;
>  
> +       if (num_online_cpus() <= 1) 
> +               return -EINVAL;

We actually know if there SMT on the system or not, which is much better
indication still:

	if (!static_branch_likely(&sched_smt_present))
		return -EINVAL;

>         if (tg->tagged == !!val)
>                 return 0;
>  
> 
> 
> 
> --