From: Steven Rostedt <rostedt@goodmis.org>
To: Daniel Bristot de Oliveira <daniel@bristot.me>
Cc: Christoph Lameter <cl@linux.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/rt: RT_RUNTIME_GREED sched feature
Date: Mon, 7 Nov 2016 15:44:01 -0500 [thread overview]
Message-ID: <20161107154401.16f0214e@gandalf.local.home> (raw)
In-Reply-To: <c46a03ef-89f5-b0c1-5886-e77266dc9a40@bristot.me>
On Mon, 7 Nov 2016 21:33:02 +0100
Daniel Bristot de Oliveira <daniel@bristot.me> wrote:
> On 11/07/2016 09:16 PM, Steven Rostedt wrote:
> > I'm confused? Are you saying that RR tasks don't get throttled in the
> > current code? That sounds like a bug to me.
>
> If the RT_RUNTIME_SHARING is enabled, the CPU in which the RR tasks are
> running (and pinned) will borrow RT runtime from another CPU, allowing
> the RR tasks to run forever. For example:
>
> [root@kiron debug]# cat /proc/sched_debug | grep rt_runtime
> .rt_runtime : 950.000000
> .rt_runtime : 950.000000
> .rt_runtime : 950.000000
> .rt_runtime : 950.000000
> [root@kiron debug]# echo RT_RUNTIME_SHARE > sched_features
> [root@kiron debug]# taskset -c 2 chrt -r 5 /home/bristot/f &
> [1] 23908
> [root@kiron debug]# taskset -c 2 chrt -r 5 /home/bristot/f &
> [2] 23915
> [root@kiron debug]# cat /proc/sched_debug | grep rt_runtime
> .rt_runtime : 900.000000
> .rt_runtime : 950.000000
> .rt_runtime : 1000.000000
> .rt_runtime : 950.000000
>
> You see? the rt_runtime of the CPU 2 was borrowed time from CPU 0.
>
> It is not a BUG but a feature (no jokes haha). With RT_RUNTIME_SHARE,
> the rt_runtime is such a global runtime. It works fine for tasks that
> can migrate... but that is not the case for per-cpu kworkers.
This still looks like a bug, or not the expected result. Perhaps we
shouldn't share when tasks are pinned. It doesn't make sense. It's like
pinning two deadline tasks to the same CPU and giving them 100% of that
CPU and saying that it's really just 1/nr_cpus of usage, which would
have the same effect.
OK, it appears this is specific to RT_RUNTIME_SHARE which is what
causes this strange behavior, and even more rational to make this a
default option and perhaps even turn RT_RUNTIME_SHARE off by default.
-- Steve
next prev parent reply other threads:[~2016-11-07 20:44 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-07 8:17 [PATCH] sched/rt: RT_RUNTIME_GREED sched feature Daniel Bristot de Oliveira
2016-11-07 10:31 ` Tommaso Cucinotta
2016-11-07 13:51 ` Daniel Bristot de Oliveira
2016-11-07 18:03 ` Tommaso Cucinotta
2016-11-07 18:06 ` Luca Abeni
2016-11-08 7:55 ` luca abeni
2016-11-08 10:30 ` Juri Lelli
2016-11-07 16:55 ` Christoph Lameter
2016-11-07 18:32 ` Steven Rostedt
2016-11-07 18:49 ` Daniel Bristot de Oliveira
2016-11-07 19:16 ` Steven Rostedt
2016-11-07 19:30 ` Christoph Lameter
2016-11-07 19:47 ` Steven Rostedt
2016-11-07 19:54 ` Christoph Lameter
2016-11-07 20:00 ` Steven Rostedt
2016-11-07 20:06 ` Daniel Bristot de Oliveira
2016-11-07 20:16 ` Steven Rostedt
2016-11-07 20:33 ` Daniel Bristot de Oliveira
2016-11-07 20:44 ` Steven Rostedt [this message]
2016-11-08 9:22 ` [PATCH] sched/rt: Change default setup for RT THROTTLING Daniel Bristot de Oliveira
2016-11-08 23:42 ` [PATCH] sched/rt: RT_RUNTIME_GREED sched feature Christoph Lameter
2016-11-07 18:22 ` Clark Williams
2016-11-07 18:30 ` Steven Rostedt
2016-11-07 18:38 ` Daniel Bristot de Oliveira
2016-11-07 18:39 ` Clark Williams
2016-11-08 11:59 ` Peter Zijlstra
2016-11-08 14:07 ` Steven Rostedt
2016-11-08 16:51 ` Peter Zijlstra
2016-11-08 17:17 ` Steven Rostedt
2016-11-08 18:05 ` Peter Zijlstra
2016-11-08 19:29 ` Daniel Bristot de Oliveira
2016-11-08 19:50 ` Peter Zijlstra
2016-11-09 13:33 ` Daniel Bristot de Oliveira
[not found] ` <CAA7rmPF0nQb9721MQWurRCy7E3X46hAy2qV=joK=z5U-t70NOg@mail.gmail.com>
2016-11-11 18:46 ` Christoph Lameter
2016-11-11 22:53 ` Peter Zijlstra
2016-11-13 18:53 ` Christoph Lameter
2016-11-14 9:20 ` Peter Zijlstra
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