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Date:   Fri, 26 Apr 2019 10:19:15 -0400
From:   Phil Auld <pauld@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Vineeth Remanan Pillai <vpillai@digitalocean.com>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, mingo@kernel.org,
        tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging
 interface
Message-ID: <20190426141915.GC16477@lorien.usersys.redhat.com>
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On Fri, Apr 26, 2019 at 04:13:07PM +0200 Peter Zijlstra wrote:
> 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;
> >  
> > 
> > 
> > 
> > -- 

Yeah, I thought there was probably a better check.

Thanks!

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