From: Khalid Aziz <khalid.aziz@oracle.com>
To: "H. Peter Anvin" <hpa@zytor.com>,
tglx@linutronix.de, Ingo Molnar <mingo@kernel.org>,
peterz@infradead.org, akpm@linux-foundation.org,
andi.kleen@intel.com, rob@landley.net, viro@zeniv.linux.org.uk,
oleg@redhat.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC] [PATCH] Pre-emption control for userspace
Date: Tue, 04 Mar 2014 14:39:48 -0700 [thread overview]
Message-ID: <53164824.3000704@oracle.com> (raw)
In-Reply-To: <531641A8.40306@zytor.com>
On 03/04/2014 02:12 PM, H. Peter Anvin wrote:
>
> Shades of the Android wakelocks, no?
>
> This seems to effectively give userspace an option to turn preemptive
> multitasking into cooperative multitasking, which of course is
> unacceptable for a privileged process (the same reason why unprivileged
> processes aren't allowed to run at above-normal priority, including RT
> priority.)
>
> I have several issues with this interface:
>
> 1. First, a process needs to know if it *should* have been preempted
> before it calls sched_yield(). So there needs to be a second flag set
> by the scheduler when granting amnesty.
Good idea. I like it. I will add it.
>
> 2. A process which fails to call sched_yield() after being granted
> amnesty must be penalized.
I agree. Is it fair to say that such a process sees the penalty by being
charged that extra timeslice and being pushed to the right side of RB
tree since its p->se.vruntime would have gone up, which then delays the
time when it can get CPU again? I am open to adding a more explicit
penalty - maybe deny its next preemption delay request if it failed to
call sched_yield() the last time when it should have?
>
> 3. I'm not keen on occupying a full page for this. I'm wondering if
> doing a pointer into user space, futex-style, might make more sense.
> The downside, of course, is what happens if the page being pointed to is
> swapped out.
Using a full page for what is effectively a single bit flag does not sit
well with me either. Doing it through proc forces minimum size of a page
(please correct me there if I am wrong). I will explore your idea some
more to see if that can be made to work.
>
> Keep in mind this HAS to be per thread.
>
Thanks, hpa!
--
Khalid
next prev parent reply other threads:[~2014-03-04 21:41 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-03 18:07 [RFC] [PATCH] Pre-emption control for userspace Khalid Aziz
2014-03-03 21:51 ` Davidlohr Bueso
2014-03-03 23:29 ` Khalid Aziz
2014-03-04 13:56 ` Oleg Nesterov
2014-03-04 17:44 ` Khalid Aziz
2014-03-04 18:38 ` Al Viro
2014-03-04 19:01 ` Khalid Aziz
2014-03-04 19:03 ` Oleg Nesterov
2014-03-04 20:14 ` Khalid Aziz
2014-03-05 14:38 ` Oleg Nesterov
2014-03-05 16:12 ` Oleg Nesterov
2014-03-05 17:10 ` Khalid Aziz
2014-03-04 21:12 ` H. Peter Anvin
2014-03-04 21:39 ` Khalid Aziz [this message]
2014-03-04 22:23 ` One Thousand Gnomes
2014-03-04 22:44 ` Khalid Aziz
2014-03-05 0:39 ` Thomas Gleixner
2014-03-05 0:51 ` Andi Kleen
2014-03-05 11:10 ` Peter Zijlstra
2014-03-05 17:29 ` Khalid Aziz
2014-03-05 19:58 ` Khalid Aziz
2014-03-06 9:57 ` Peter Zijlstra
2014-03-06 16:08 ` Khalid Aziz
2014-03-06 11:14 ` Thomas Gleixner
2014-03-06 16:32 ` Khalid Aziz
2014-03-05 14:54 ` Oleg Nesterov
2014-03-05 15:56 ` Andi Kleen
2014-03-05 16:36 ` Oleg Nesterov
2014-03-05 17:22 ` Khalid Aziz
2014-03-05 23:13 ` David Lang
2014-03-05 23:48 ` Khalid Aziz
2014-03-05 23:56 ` H. Peter Anvin
2014-03-06 0:02 ` Khalid Aziz
2014-03-06 0:13 ` H. Peter Anvin
2014-03-05 23:59 ` David Lang
2014-03-06 0:17 ` Khalid Aziz
2014-03-06 0:36 ` David Lang
2014-03-06 1:22 ` Khalid Aziz
2014-03-06 14:23 ` David Lang
2014-03-06 12:13 ` Kevin Easton
2014-03-06 13:59 ` Peter Zijlstra
2014-03-06 22:41 ` Andi Kleen
2014-03-06 14:25 ` David Lang
2014-03-06 16:12 ` Khalid Aziz
2014-03-06 13:24 ` Rasmus Villemoes
2014-03-06 13:34 ` Peter Zijlstra
2014-03-06 13:45 ` Rasmus Villemoes
2014-03-06 14:02 ` Peter Zijlstra
2014-03-06 14:33 ` Thomas Gleixner
2014-03-06 14:34 ` H. Peter Anvin
2014-03-06 14:04 ` Thomas Gleixner
2014-03-25 17:17 ` [PATCH v2] " Khalid Aziz
2014-03-25 17:44 ` Andrew Morton
2014-03-25 17:56 ` Khalid Aziz
2014-03-25 18:14 ` Andrew Morton
2014-03-25 17:46 ` Oleg Nesterov
2014-03-25 17:59 ` Khalid Aziz
2014-03-25 18:20 ` Andi Kleen
2014-03-25 18:47 ` Khalid Aziz
2014-03-25 19:47 ` Andi Kleen
2014-03-25 18:59 ` Eric W. Biederman
2014-03-25 19:15 ` Khalid Aziz
2014-03-25 20:31 ` Eric W. Biederman
2014-03-25 21:37 ` Khalid Aziz
2014-03-26 6:03 ` Mike Galbraith
2014-03-25 23:01 ` [RFC] [PATCH] " Davidlohr Bueso
2014-03-25 23:29 ` Khalid Aziz
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