Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology
Date	2016-09-08 20:30 +0200
Message-ID	<sfcff-S4-7@gated-at.bofh.it> (permalink)
References	<scHpf-70l-11@gated-at.bofh.it> <scHpf-70l-9@gated-at.bofh.it> <sf2zg-3eC-19@gated-at.bofh.it> <sfbVT-HP-9@gated-at.bofh.it>
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On Thu, Sep 08, 2016 at 11:09:28AM -0700, Tim Chen wrote:
> On Thu, Sep 08, 2016 at 09:59:55AM +0200, Peter Zijlstra wrote:
> > I think there's a race here, if two tasks were to write to the sysctl
> > they'd both change the value before getting stuck on the mutex in
> > enable_sched_itmt().
> > 
> > One way around that is doing something like:
> > 
> > 
> > 	struct ctl_table t;
> > 	int val = sysctl_sched_itmt_enabled;
> > 
> > 	t = *table;
> > 	t.data = &val;
> > 
> > 	proc_dointvec_minmax(&t, ...);
> > 
> > 	/* and update the sysctl_sched_itmt_enabled value inside the mutex */
> > 	enable_sched_itmi(val);
> 
> Peter,
> 
> Since enable_sched_itmt is only used by sched_itmt_update_handler,
> I've moved the mutex locking to sched_itmt_update_handler to eliminate
> the race condition in the code path you mentioned.

That is indeed simpler. Thanks!

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[PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> - 2016-09-01 23:10 +0200
  Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Peter Zijlstra <peterz@infradead.org> - 2016-09-08 10:10 +0200
    Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Tim Chen <tim.c.chen@linux.intel.com> - 2016-09-08 20:10 +0200
      Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> - 2016-09-08 20:30 +0200
        Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Peter Zijlstra <peterz@infradead.org> - 2016-09-08 20:40 +0200
          Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> - 2016-09-08 20:50 +0200
        Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-09-08 23:20 +0200
      Re: [PATCH v2 5/8] sched,x86: Enable Turbo Boost Max Technology Peter Zijlstra <peterz@infradead.org> - 2016-09-08 20:30 +0200

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