From: Ankur Arora <ankur.a.arora@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ankur Arora <ankur.a.arora@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de,
dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org,
tglx@linutronix.de, jon.grimm@amd.com, bharata@amd.com,
raghavendra.kt@amd.com, boris.ostrovsky@oracle.com,
konrad.wilk@oracle.com, jgross@suse.com,
andrew.cooper3@citrix.com
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED
Date: Mon, 11 Sep 2023 10:04:17 -0700 [thread overview]
Message-ID: <87h6o01w1a.fsf@oracle.com> (raw)
In-Reply-To: <20230911150410.GC9098@noisy.programming.kicks-ass.net>
Peter Zijlstra <peterz@infradead.org> writes:
> On Sun, Sep 10, 2023 at 11:32:32AM -0700, Linus Torvalds wrote:
>
>> I was hoping that we'd have some generic way to deal with this where
>> we could just say "this thing is reschedulable", and get rid of - or
>> at least not increasingly add to - the cond_resched() mess.
>
> Isn't that called PREEMPT=y ? That tracks precisely all the constraints
> required to know when/if we can preempt.
>
> The whole voluntary preempt model is basically the traditional
> co-operative preemption model and that fully relies on manual yields.
Yeah, but as Linus says, this means a lot of code is just full of
cond_resched(). For instance a loop the process_huge_page() uses
this pattern:
for (...) {
cond_resched();
clear_page(i);
cond_resched();
clear_page(j);
}
> The problem with the REP prefix (and Xen hypercalls) is that
> they're long running instructions and it becomes fundamentally
> impossible to put a cond_resched() in.
>
>> Yes. I'm starting to think that that the only sane solution is to
>> limit cases that can do this a lot, and the "instruciton pointer
>> region" approach would certainly work.
>
> From a code locality / I-cache POV, I think a sorted list of
> (non overlapping) ranges might be best.
Yeah, agreed. There are a few problems with doing that though.
I was thinking of using a check of this kind to schedule out when
it is executing in this "reschedulable" section:
!preempt_count() && in_resched_function(regs->rip);
For preemption=full, this should mostly work.
For preemption=voluntary, though this'll only work with out-of-line
locks, not if the lock is inlined.
(Both, should have problems with __this_cpu_* and the like, but
maybe we can handwave that away with sparse/objtool etc.)
How expensive would be always having PREEMPT_COUNT=y?
--
ankur
next prev parent reply other threads:[~2023-09-11 22:16 UTC|newest]
Thread overview: 214+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-30 18:49 [PATCH v2 0/9] x86/clear_huge_page: multi-page clearing Ankur Arora
2023-08-30 18:49 ` [PATCH v2 1/9] mm/clear_huge_page: allow arch override for clear_huge_page() Ankur Arora
2023-08-30 18:49 ` [PATCH v2 2/9] mm/huge_page: separate clear_huge_page() and copy_huge_page() Ankur Arora
2023-08-30 18:49 ` [PATCH v2 3/9] mm/huge_page: cleanup clear_/copy_subpage() Ankur Arora
2023-09-08 13:09 ` Matthew Wilcox
2023-09-11 17:22 ` Ankur Arora
2023-08-30 18:49 ` [PATCH v2 4/9] x86/clear_page: extend clear_page*() for multi-page clearing Ankur Arora
2023-09-08 13:11 ` Matthew Wilcox
2023-08-30 18:49 ` [PATCH v2 5/9] x86/clear_page: add clear_pages() Ankur Arora
2023-08-30 18:49 ` [PATCH v2 6/9] x86/clear_huge_page: multi-page clearing Ankur Arora
2023-08-31 18:26 ` kernel test robot
2023-09-08 12:38 ` Peter Zijlstra
2023-09-13 6:43 ` Raghavendra K T
2023-08-30 18:49 ` [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED Ankur Arora
2023-09-08 7:02 ` Peter Zijlstra
2023-09-08 17:15 ` Linus Torvalds
2023-09-08 22:50 ` Peter Zijlstra
2023-09-09 5:15 ` Linus Torvalds
2023-09-09 6:39 ` Ankur Arora
2023-09-09 9:11 ` Peter Zijlstra
2023-09-09 20:04 ` Ankur Arora
2023-09-09 5:30 ` Ankur Arora
2023-09-09 9:12 ` Peter Zijlstra
2023-09-09 20:15 ` Ankur Arora
2023-09-09 21:16 ` Linus Torvalds
2023-09-10 3:48 ` Ankur Arora
2023-09-10 4:35 ` Linus Torvalds
2023-09-10 10:01 ` Ankur Arora
2023-09-10 18:32 ` Linus Torvalds
2023-09-11 15:04 ` Peter Zijlstra
2023-09-11 16:29 ` andrew.cooper3
2023-09-11 17:04 ` Ankur Arora [this message]
2023-09-12 8:26 ` Peter Zijlstra
2023-09-12 12:24 ` Phil Auld
2023-09-12 12:33 ` Matthew Wilcox
2023-09-18 23:42 ` Thomas Gleixner
2023-09-19 1:57 ` Linus Torvalds
2023-09-19 8:03 ` Ingo Molnar
2023-09-19 8:43 ` Ingo Molnar
2023-09-19 13:43 ` Thomas Gleixner
2023-09-19 13:25 ` Thomas Gleixner
2023-09-19 12:30 ` Thomas Gleixner
2023-09-19 13:00 ` Arches that don't support PREEMPT Matthew Wilcox
2023-09-19 13:00 ` Matthew Wilcox
2023-09-19 13:00 ` Matthew Wilcox
2023-09-19 13:34 ` Geert Uytterhoeven
2023-09-19 13:34 ` Geert Uytterhoeven
2023-09-19 13:34 ` Geert Uytterhoeven
2023-09-19 13:37 ` John Paul Adrian Glaubitz
2023-09-19 13:37 ` John Paul Adrian Glaubitz
2023-09-19 13:37 ` John Paul Adrian Glaubitz
2023-09-19 13:42 ` Peter Zijlstra
2023-09-19 13:42 ` Peter Zijlstra
2023-09-19 13:42 ` Peter Zijlstra
2023-09-19 13:48 ` John Paul Adrian Glaubitz
2023-09-19 13:48 ` John Paul Adrian Glaubitz
2023-09-19 13:48 ` John Paul Adrian Glaubitz
2023-09-19 14:16 ` Peter Zijlstra
2023-09-19 14:16 ` Peter Zijlstra
2023-09-19 14:16 ` Peter Zijlstra
2023-09-19 14:24 ` John Paul Adrian Glaubitz
2023-09-19 14:24 ` John Paul Adrian Glaubitz
2023-09-19 14:24 ` John Paul Adrian Glaubitz
2023-09-19 14:32 ` Matthew Wilcox
2023-09-19 14:32 ` Matthew Wilcox
2023-09-19 14:32 ` Matthew Wilcox
2023-09-19 15:31 ` Steven Rostedt
2023-09-19 15:31 ` Steven Rostedt
2023-09-19 15:31 ` Steven Rostedt
2023-09-20 14:38 ` Anton Ivanov
2023-09-20 14:38 ` Anton Ivanov
2023-09-20 14:38 ` Anton Ivanov
2023-09-21 12:20 ` Arnd Bergmann
2023-09-21 12:20 ` Arnd Bergmann
2023-09-21 12:20 ` Arnd Bergmann
2023-09-19 14:17 ` Thomas Gleixner
2023-09-19 14:17 ` Thomas Gleixner
2023-09-19 14:17 ` Thomas Gleixner
2023-09-19 14:50 ` H. Peter Anvin
2023-09-19 14:50 ` H. Peter Anvin
2023-09-19 14:50 ` H. Peter Anvin
2023-09-19 14:57 ` Matt Turner
2023-09-19 14:57 ` Matt Turner
2023-09-19 14:57 ` Matt Turner
2023-09-19 17:09 ` Ulrich Teichert
2023-09-19 17:09 ` Ulrich Teichert
2023-09-19 17:25 ` Linus Torvalds
2023-09-19 17:25 ` Linus Torvalds
2023-09-19 17:25 ` Linus Torvalds
2023-09-19 17:58 ` John Paul Adrian Glaubitz
2023-09-19 17:58 ` John Paul Adrian Glaubitz
2023-09-19 17:58 ` John Paul Adrian Glaubitz
2023-09-19 18:31 ` Thomas Gleixner
2023-09-19 18:31 ` Thomas Gleixner
2023-09-19 18:31 ` Thomas Gleixner
2023-09-19 18:38 ` Steven Rostedt
2023-09-19 18:38 ` Steven Rostedt
2023-09-19 18:38 ` Steven Rostedt
2023-09-19 18:52 ` Linus Torvalds
2023-09-19 18:52 ` Linus Torvalds
2023-09-19 18:52 ` Linus Torvalds
2023-09-19 19:53 ` Thomas Gleixner
2023-09-19 19:53 ` Thomas Gleixner
2023-09-19 19:53 ` Thomas Gleixner
2023-09-20 7:32 ` Ingo Molnar
2023-09-20 7:32 ` Ingo Molnar
2023-09-20 7:32 ` Ingo Molnar
2023-09-20 7:29 ` Ingo Molnar
2023-09-20 7:29 ` Ingo Molnar
2023-09-20 7:29 ` Ingo Molnar
2023-09-20 8:26 ` Thomas Gleixner
2023-09-20 8:26 ` Thomas Gleixner
2023-09-20 8:26 ` Thomas Gleixner
2023-09-20 10:37 ` David Laight
2023-09-20 10:37 ` David Laight
2023-09-20 10:37 ` David Laight
2023-09-19 14:21 ` Anton Ivanov
2023-09-19 14:21 ` Anton Ivanov
2023-09-19 14:21 ` Anton Ivanov
2023-09-19 15:17 ` Thomas Gleixner
2023-09-19 15:17 ` Thomas Gleixner
2023-09-19 15:17 ` Thomas Gleixner
2023-09-19 15:21 ` Anton Ivanov
2023-09-19 15:21 ` Anton Ivanov
2023-09-19 15:21 ` Anton Ivanov
2023-09-19 16:22 ` Richard Weinberger
2023-09-19 16:22 ` Richard Weinberger
2023-09-19 16:22 ` Richard Weinberger
2023-09-19 16:41 ` Anton Ivanov
2023-09-19 16:41 ` Anton Ivanov
2023-09-19 16:41 ` Anton Ivanov
2023-09-19 17:33 ` Thomas Gleixner
2023-09-19 17:33 ` Thomas Gleixner
2023-09-19 17:33 ` Thomas Gleixner
2023-10-06 14:51 ` Geert Uytterhoeven
2023-10-06 14:51 ` Geert Uytterhoeven
2023-09-20 14:22 ` [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED Ankur Arora
2023-09-20 20:51 ` Thomas Gleixner
2023-09-21 0:14 ` Thomas Gleixner
2023-09-21 0:58 ` Ankur Arora
2023-09-21 2:12 ` Thomas Gleixner
2023-09-20 23:58 ` Thomas Gleixner
2023-09-21 0:57 ` Ankur Arora
2023-09-21 2:02 ` Thomas Gleixner
2023-09-21 4:16 ` Ankur Arora
2023-09-21 13:59 ` Steven Rostedt
2023-09-21 16:00 ` Linus Torvalds
2023-09-21 22:55 ` Thomas Gleixner
2023-09-23 1:11 ` Thomas Gleixner
2023-10-02 14:15 ` Steven Rostedt
2023-10-02 16:13 ` Thomas Gleixner
2023-10-18 1:03 ` Paul E. McKenney
2023-10-18 12:09 ` Ankur Arora
2023-10-18 17:51 ` Paul E. McKenney
2023-10-18 22:53 ` Thomas Gleixner
2023-10-18 23:25 ` Paul E. McKenney
2023-10-18 13:16 ` Thomas Gleixner
2023-10-18 14:31 ` Steven Rostedt
2023-10-18 17:55 ` Paul E. McKenney
2023-10-18 18:00 ` Steven Rostedt
2023-10-18 18:13 ` Paul E. McKenney
2023-10-19 12:37 ` Daniel Bristot de Oliveira
2023-10-19 17:08 ` Paul E. McKenney
2023-10-18 17:19 ` Paul E. McKenney
2023-10-18 17:41 ` Steven Rostedt
2023-10-18 17:59 ` Paul E. McKenney
2023-10-18 20:15 ` Ankur Arora
2023-10-18 20:42 ` Paul E. McKenney
2023-10-19 0:21 ` Thomas Gleixner
2023-10-19 19:13 ` Paul E. McKenney
2023-10-20 21:59 ` Paul E. McKenney
2023-10-20 22:56 ` Ankur Arora
2023-10-20 23:36 ` Paul E. McKenney
2023-10-21 1:05 ` Ankur Arora
2023-10-21 2:08 ` Paul E. McKenney
2023-10-24 12:15 ` Thomas Gleixner
2023-10-24 18:59 ` Paul E. McKenney
2023-09-23 22:50 ` Thomas Gleixner
2023-09-24 0:10 ` Thomas Gleixner
2023-09-24 7:19 ` Matthew Wilcox
2023-09-24 7:55 ` Thomas Gleixner
2023-09-24 10:29 ` Matthew Wilcox
2023-09-25 0:13 ` Ankur Arora
2023-10-06 13:01 ` Geert Uytterhoeven
2023-09-19 7:21 ` Ingo Molnar
2023-09-19 19:05 ` Ankur Arora
2023-10-24 14:34 ` Steven Rostedt
2023-10-25 1:49 ` Steven Rostedt
2023-10-26 7:50 ` Sergey Senozhatsky
2023-10-26 12:48 ` Steven Rostedt
2023-09-11 16:48 ` Steven Rostedt
2023-09-11 20:50 ` Linus Torvalds
2023-09-11 21:16 ` Linus Torvalds
2023-09-12 7:20 ` Peter Zijlstra
2023-09-12 7:38 ` Ingo Molnar
2023-09-11 22:20 ` Steven Rostedt
2023-09-11 23:10 ` Ankur Arora
2023-09-11 23:16 ` Steven Rostedt
2023-09-12 16:30 ` Linus Torvalds
2023-09-12 3:27 ` Matthew Wilcox
2023-09-12 16:20 ` Linus Torvalds
2023-09-19 3:21 ` Andy Lutomirski
2023-09-19 9:20 ` Thomas Gleixner
2023-09-19 9:49 ` Ingo Molnar
2023-08-30 18:49 ` [PATCH v2 8/9] irqentry: define irqentry_exit_allow_resched() Ankur Arora
2023-09-08 12:42 ` Peter Zijlstra
2023-09-11 17:24 ` Ankur Arora
2023-08-30 18:49 ` [PATCH v2 9/9] x86/clear_huge_page: make clear_contig_region() preemptible Ankur Arora
2023-09-08 12:45 ` Peter Zijlstra
2023-09-03 8:14 ` [PATCH v2 0/9] x86/clear_huge_page: multi-page clearing Mateusz Guzik
2023-09-05 22:14 ` Ankur Arora
2023-09-08 2:18 ` Raghavendra K T
2023-09-05 1:06 ` Raghavendra K T
2023-09-05 19:36 ` Ankur Arora
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