From: Viresh Kumar <viresh.kumar@linaro.org>
To: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: rjw@rjwysocki.net, ego@linux.vnet.ibm.com, paulus@samba.org,
linux-kernel@vger.kernel.org, shilpa.bhat@linux.vnet.ibm.com,
linux-pm@vger.kernel.org
Subject: Re: [RFC PATCH] cpufreq/hotplug: Fix cpu-hotplug cpufreq race conditions
Date: Tue, 2 Jun 2015 11:09:56 +0530 [thread overview]
Message-ID: <20150602053956.GD10443@linux> (raw)
In-Reply-To: <556D3FAA.3080703@linux.vnet.ibm.com>
On 02-06-15, 11:01, Preeti U Murthy wrote:
> How will a policy lock help here at all, when cpus from multiple
> policies are calling into __cpufreq_governor() ? How will a policy lock
> serialize their entry into cpufreq_governor_dbs() ?
So different policies don't really depend on each other. The only
thing common to them are the governor's sysfs files (only if
governor-per-policy isn't set, i.e. in your case). Those sysfs files
and their kernel counterpart variables aren't touched unless all the
policies have EXITED. All these START/STOP calls touch only the data
relevant to those policies only.
In case of per-policy governors, even those sysfs files are separate
for each policy.
And so a policy lock should be sufficient, rest should be handled
within the governors with locks or whatever.
> > These band-aid wouldn't take us anywhere.
>
> Why do you say that the approach mentioned in this patch is a bandaid ?
> The patch ensures that there are no interruptions in a logical sequence
> of calls into cpufreq_governor_dbs(), as it should be.
Because this happened as we are forced to drop the policy-locks.
That's the real problem. This whole thing should be performed under
locks, instead of setting variables to mark governor busy under locks.
--
viresh
next prev parent reply other threads:[~2015-06-02 5:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-01 6:40 [RFC PATCH] cpufreq/hotplug: Fix cpu-hotplug cpufreq race conditions Preeti U Murthy
2015-06-01 7:19 ` Viresh Kumar
2015-06-01 7:55 ` Preeti U Murthy
2015-06-02 5:31 ` Preeti U Murthy
2015-06-02 5:39 ` Viresh Kumar [this message]
2015-06-02 6:03 ` Preeti U Murthy
2015-06-02 6:11 ` Viresh Kumar
2015-06-02 6:20 ` Preeti U Murthy
2015-06-02 6:27 ` Viresh Kumar
2015-06-02 6:56 ` Preeti U Murthy
2015-06-02 7:07 ` Viresh Kumar
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