linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Paul Turner <pjt@google.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
	Joel Fernandes <joelaf@google.com>,
	Steve Muckle <smuckle@google.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting
Date: Thu, 16 Aug 2018 14:32:49 +0100	[thread overview]
Message-ID: <20180816133249.GA2964@e110439-lin> (raw)
In-Reply-To: <ccd9c53f-55f7-a285-39eb-4303888dafcd@arm.com>

Hi Dietmar!

On 15-Aug 12:59, Dietmar Eggemann wrote:
> On 08/15/2018 12:54 PM, Patrick Bellasi wrote:
> >On 15-Aug 11:37, Dietmar Eggemann wrote:
> >>On 08/14/2018 06:49 PM, Patrick Bellasi wrote:

[...]

> >>If this is only for testing/debugging, I would suggest a simple one line
> >>BUG_ON()
> >
> >These are (eventually) considered as recoverable errors... thus,
> >AFAIK, using BUG_ON is overkilling and discouraged:
> >   https://elixir.bootlin.com/linux/latest/source/include/asm-generic/bug.h#L42
> 
> Not sure about that. If this refcounting is out of sync, that's indicating a
> serious issue here for me which should be fixed.

Well, refconting seems quite ok to me, we always inc/dec under RQ
locking and it's a per-CPU variable.

The warning is there to report issues on further testing as well as to
be safe with respect to possible future modifications of the code.

> >>You find CONFIG_SCHED_DEBUG=y in production kernels as well.
> >
> >AFAIK, that setting is discouraged for production kernels...
> >Moreover, it's still better to WARN sometimes on a production kernel
> >the crash the device, isnt't it?
> 
> IMHO, if this is something which should not happen at all, a BUG_ON() is the
> right thing to do here.

I don't agree on that. I agree it should not happen but since it's a
recoverable error it think we should not panic.

There are really few BUG_ON() in core.c and they are all for much more
serious issues than a (eventually) broken refcount.

IMHO instead an (unlikely) inconsistent refcont for an "optional
optimization" on "frequency selection" is not such a critical
failure worth a device crash.

> And you get the call stack to investigate why it hit.

We can always add a stack dump if we notice the warning.

But, since we do not agree on that point, I would say we should better
wait for what the maintainers prefers.

Best,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

  reply	other threads:[~2018-08-16 13:33 UTC|newest]

Thread overview: 82+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-06 16:39 [PATCH v3 00/14] Add utilization clamping support Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 01/14] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi
2018-08-06 16:50   ` Randy Dunlap
2018-08-09  8:39     ` Patrick Bellasi
2018-08-09 15:20       ` Randy Dunlap
2018-08-07  9:59   ` Juri Lelli
2018-08-13 12:14     ` Patrick Bellasi
2018-08-13 12:27       ` Juri Lelli
2018-08-07 12:35   ` Juri Lelli
2018-08-09  9:14     ` Patrick Bellasi
2018-08-09  9:50       ` Juri Lelli
2018-08-09 15:23         ` Patrick Bellasi
2018-08-10  7:50           ` Juri Lelli
2018-08-17 10:34           ` Quentin Perret
2018-08-17 10:57             ` Patrick Bellasi
2018-08-17 11:14               ` Quentin Perret
2018-08-06 16:39 ` [PATCH v3 02/14] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-14 11:25   ` Pavan Kondeti
2018-08-14 15:21     ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting Patrick Bellasi
2018-08-14 15:44   ` Dietmar Eggemann
2018-08-14 16:49     ` Patrick Bellasi
2018-08-15  9:37       ` Dietmar Eggemann
2018-08-15 10:54         ` Patrick Bellasi
2018-08-15 10:59           ` Dietmar Eggemann
2018-08-16 13:32             ` Patrick Bellasi [this message]
2018-08-16 13:37               ` Quentin Perret
2018-08-16 13:45                 ` Dietmar Eggemann
2018-08-16 14:21                   ` Quentin Perret
2018-08-16 15:00                     ` Dietmar Eggemann
2018-08-17 11:04   ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 04/14] sched/core: uclamp: update CPU's refcount on clamp changes Patrick Bellasi
2018-08-15 15:02   ` Dietmar Eggemann
2018-08-16 13:22     ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 05/14] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi
2018-08-08 13:18   ` Vincent Guittot
2018-08-09 15:30     ` Patrick Bellasi
2018-08-15 15:30   ` Dietmar Eggemann
2018-08-16 13:53     ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
2018-08-07 13:26   ` Juri Lelli
2018-08-09 15:34     ` Patrick Bellasi
2018-08-09 16:03       ` Vincent Guittot
2018-08-13 10:12         ` Patrick Bellasi
2018-08-13 10:50           ` Juri Lelli
2018-08-13 12:07           ` Vincent Guittot
2018-08-13 12:09             ` Vincent Guittot
2018-08-13 12:49             ` Patrick Bellasi
2018-08-13 14:06               ` Vincent Guittot
2018-08-13 15:01                 ` Patrick Bellasi
2018-08-16 10:34                   ` Dietmar Eggemann
2018-08-16 13:40                     ` Patrick Bellasi
2018-08-07 13:54   ` Quentin Perret
2018-08-09 15:41     ` Patrick Bellasi
2018-08-09 15:55       ` Quentin Perret
2018-08-13 10:17         ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX Patrick Bellasi
2018-08-16 15:43   ` Dietmar Eggemann
2018-08-16 16:47     ` Patrick Bellasi
2018-08-16 17:10       ` Dietmar Eggemann
2018-08-16 17:27         ` Patrick Bellasi
2018-08-16 17:20   ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 08/14] sched/core: uclamp: extend cpu's cgroup controller Patrick Bellasi
2018-08-17 12:21   ` Dietmar Eggemann
2018-08-17 14:24     ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps Patrick Bellasi
2018-08-16  9:09   ` Pavan Kondeti
2018-08-16 14:07     ` Patrick Bellasi
2018-08-17 13:43   ` Dietmar Eggemann
2018-08-17 14:45     ` Patrick Bellasi
2018-08-17 15:50       ` Dietmar Eggemann
2018-08-20 10:01         ` Dietmar Eggemann
2018-08-20 12:28           ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 10/14] sched/core: uclamp: map TG's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 11/14] sched/core: uclamp: use TG's clamps to restrict Task's clamps Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 12/14] sched/core: uclamp: add system default clamps Patrick Bellasi
2018-08-16  9:13   ` Pavan Kondeti
2018-08-16 14:37     ` Patrick Bellasi
2018-08-20 10:18   ` Dietmar Eggemann
2018-08-20 12:27     ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 13/14] sched/core: uclamp: update CPU's refcount on TG's clamp changes Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 14/14] sched/core: uclamp: use percentage clamp values Patrick Bellasi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180816133249.GA2964@e110439-lin \
    --to=patrick.bellasi@arm.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=joelaf@google.com \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=morten.rasmussen@arm.com \
    --cc=peterz@infradead.org \
    --cc=pjt@google.com \
    --cc=rafael.j.wysocki@intel.com \
    --cc=smuckle@google.com \
    --cc=surenb@google.com \
    --cc=tj@kernel.org \
    --cc=tkjos@google.com \
    --cc=vincent.guittot@linaro.org \
    --cc=viresh.kumar@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).