From: Viresh Kumar <viresh.kumar@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Saravana Kannan <skannan@codeaurora.org>,
Shilpa Bhat <shilpabhatppc@gmail.com>,
Juri Lelli <juri.lelli@arm.com>,
Rafael Wysocki <rjw@rjwysocki.net>,
Lists linaro-kernel <linaro-kernel@lists.linaro.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Michael Turquette <mturquette@baylibre.com>,
Steve Muckle <steve.muckle@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
dietmar.eggemann@arm.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups
Date: Fri, 5 Feb 2016 08:14:28 +0530 [thread overview]
Message-ID: <20160205024428.GB3068@vireshk> (raw)
In-Reply-To: <CAJZ5v0hG2CickrbnTn8qJdFHJZ4cuZg1nxJ=8OXN8YFuw=qSFQ@mail.gmail.com>
On 04-02-16, 19:18, Rafael J. Wysocki wrote:
> On Thu, Feb 4, 2016 at 6:44 PM, Saravana Kannan <skannan@codeaurora.org> wrote:
> > On 02/04/2016 09:43 AM, Saravana Kannan wrote:
> >> No no no no! Let's not open up this can of worms of queuing up the work
> >> to handle a write to a sysfs file. It *MIGHT* work for this specific
> >> tunable (I haven't bothered to analyze), but this makes it impossible to
> >> return a useful/proper error value.
> >
> >
> > Sent too soon. Not only that, but it can also cause the writes to the sysfs
> > files to get processed in a different order and I don't know what other
> > issues/races THAT will open up.
>
> Well, I don't like this too.
I expected similar responses only, so no surprises for me :)
Though there are few things I would like to tell here:
- There wouldn't be any race for updating the file, as that is done
directly from store_sampling_rate(). It updates the *real* file we
wanted to.
- What's offloaded to the work-handler is something very special about
ondemand governor and sampling rate. The same is not done for
conservative governor as well, don't know why though.
- After updating the sampling rate, we assess if we need to reschedule
the timers/workqueue to a different time for better efficiency. I
don't think there can be a race there and it can be safely done in a
work..
> I actually do have an idea about how to fix these deadlocks, but it is
> on top of my cleanup series.
I would like to hear that, if you can, to save your time. I have tried
so many different ways of fixing this yesterday and found issue
everywhere :(
--
viresh
next prev parent reply other threads:[~2016-02-05 2:44 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-03 14:02 [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 1/7] cpufreq: governor: Treat min_sampling_rate as a governor-specific tunable Viresh Kumar
2016-02-05 2:31 ` Rafael J. Wysocki
2016-02-05 2:47 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 2/7] cpufreq: governor: New sysfs show/store callbacks for governor tunables Viresh Kumar
2016-02-03 16:17 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 3/7] cpufreq: governor: Drop unused macros for creating governor tunable attributes Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 4/7] Revert "cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT" Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 5/7] cpufreq: Merge cpufreq_offline_prepare/finish routines Viresh Kumar
2016-02-03 20:21 ` Saravana Kannan
2016-02-04 1:49 ` Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 6/7] cpufreq: Call __cpufreq_governor() with policy->rwsem held Viresh Kumar
2016-02-03 14:02 ` [PATCH V2 7/7] cpufreq: Remove cpufreq_governor_lock Viresh Kumar
2016-02-04 6:43 ` Viresh Kumar
2016-02-03 15:54 ` [PATCH V2 0/7] cpufreq: governors: Fix ABBA lockups Juri Lelli
2016-02-03 16:10 ` Viresh Kumar
2016-02-03 17:20 ` Juri Lelli
2016-02-03 17:20 ` Rafael J. Wysocki
2016-02-03 23:31 ` Shilpa Bhat
2016-02-03 23:50 ` Rafael J. Wysocki
2016-02-04 5:51 ` Viresh Kumar
2016-02-04 11:09 ` Viresh Kumar
2016-02-04 17:43 ` Saravana Kannan
2016-02-04 17:44 ` Saravana Kannan
2016-02-04 18:18 ` Rafael J. Wysocki
2016-02-05 2:44 ` Viresh Kumar [this message]
2016-02-05 3:54 ` Rafael J. Wysocki
2016-02-05 9:49 ` Viresh Kumar
2016-02-08 2:20 ` Rafael J. Wysocki
2016-02-06 2:22 ` Saravana Kannan
2016-02-08 2:28 ` Rafael J. Wysocki
2016-02-09 21:02 ` Saravana Kannan
2016-02-04 6:24 ` Viresh Kumar
2016-02-04 12:17 ` Viresh Kumar
2016-02-04 20:50 ` Shilpasri G Bhat
2016-02-05 2:49 ` Viresh Kumar
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