linux-kernel - Re: [PATCH v2 2/2] perf/x86/intel: force resched when TFA sysctl is modified

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Date:   Mon, 15 Apr 2019 10:20:57 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        "Liang, Kan" <kan.liang@...el.com>, mingo@...e.hu,
        nelson.dsouza@...el.com, Jiri Olsa <jolsa@...hat.com>,
        tonyj@...e.com
Subject: Re: [PATCH v2 2/2] perf/x86/intel: force resched when TFA sysctl is modified

On Mon, Apr 15, 2019 at 8:57 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Apr 08, 2019 at 10:32:52AM -0700, Stephane Eranian wrote:
> > +static ssize_t set_sysctl_tfa(struct device *cdev,
> > +                           struct device_attribute *attr,
> > +                           const char *buf, size_t count)
> > +{
> > +     bool val;
> > +     ssize_t ret;
> > +
> > +     ret = kstrtobool(buf, &val);
> > +     if (ret)
> > +             return ret;
> > +
> > +     /* no change */
> > +     if (val == allow_tsx_force_abort)
> > +             return count;
> > +
> > +     allow_tsx_force_abort = val;
> > +
> > +     get_online_cpus();
> > +     on_each_cpu(update_tfa_sched, NULL, 1);
> > +     put_online_cpus();
> > +
> > +     return count;
> > +}
>
> So we care about concurrent writing to that file?
Not likely but we care about seeing the effects on event scheduling
before the sysctl returns.