From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>, Christoph Lameter <cl@linux.com>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
Subject: Re: [PATCH] sched/rt: RT_RUNTIME_GREED sched feature
Date: Tue, 8 Nov 2016 20:50:15 +0100 [thread overview]
Message-ID: <20161108195015.GP3117@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <f4095990-3fa0-ac2f-7277-3b8f0cdbc333@redhat.com>
On Tue, Nov 08, 2016 at 08:29:49PM +0100, Daniel Bristot de Oliveira wrote:
>
>
> On 11/08/2016 07:05 PM, Peter Zijlstra wrote:
> >> >
> >> > I know what we want to do, but there's some momentous problems that
> >> > need to be solved first.
> > Like what?
>
> The problem is that using RT_RUNTIME_SHARE a CPU will almost always
> borrow enough runtime to make a CPU intensive rt task to run forever...
> well not forever, but until the system crash because a kworker starved
> in this CPU. Kworkers are sched fair by design and users do not always
> have a way to avoid them in an isolated CPU, for example.
>
> The user then can disable RT_RUNTIME_SHARE, but then the user will have
> the CPU going idle for (period - runtime) at each period... throwing CPU
> time in the trash.
So why is this a problem? You really should not be running that much
FIFO tasks to begin with.
So I'm willing to take out (or at least default disable
RT_RUNTIME_SHARE). But other than this, this never really worked to
begin with. So it cannot be a regression. And we've lived this long with
the 'problem'.
And that means this is a 'feature' and that means I say no.
We really should be doing the right thing here, not make a bigger mess.
next prev parent reply other threads:[~2016-11-08 19:50 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
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 [this message]
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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