From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <namit@vmware.com>
Cc: Ingo Molnar <mingo@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
"H. Peter Anvin" <hpa@zytor.com>,
Linux-Next Mailing List <linux-next@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus <torvalds@linux-foundation.org>,
"minchan@kernel.org" <minchan@kernel.org>
Subject: Re: linux-next: manual merge of the akpm-current tree with the tip tree
Date: Sun, 13 Aug 2017 14:50:19 +0200 [thread overview]
Message-ID: <20170813125019.ihqjud37ytgri7bn@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <DE232310-8D7E-4074-ACFE-FE6416B13A3F@vmware.com>
On Sun, Aug 13, 2017 at 06:06:32AM +0000, Nadav Amit wrote:
> > however mm_tlb_flush_nested() is a mystery, it appears to care about
> > anything inside the range. For now rely on it doing at least _a_ PTL
> > lock instead of taking _the_ PTL lock.
>
> It does not care about “anything” inside the range, but only on situations
> in which there is at least one (same) PT that was modified by one core and
> then read by the other. So, yes, it will always be _the_ same PTL, and not
> _a_ PTL - in the cases that flush is really needed.
>
> The issue that might require additional barriers is that
> inc_tlb_flush_pending() and mm_tlb_flush_nested() are called when the PTL is
> not held. IIUC, since the release-acquire might not behave as a full memory
> barrier, this requires an explicit memory barrier.
So I'm not entirely clear about this yet.
How about:
CPU0 CPU1
tlb_gather_mmu()
lock PTLn
no mod
unlock PTLn
tlb_gather_mmu()
lock PTLm
mod
include in tlb range
unlock PTLm
lock PTLn
mod
unlock PTLn
tlb_finish_mmu()
force = mm_tlb_flush_nested(tlb->mm);
arch_tlb_finish_mmu(force);
... more ...
tlb_finish_mmu()
In this case you also want CPU1's mm_tlb_flush_nested() call to return
true, right?
But even with an smp_mb__after_atomic() at CPU0's tlg_bather_mmu()
you're not guaranteed CPU1 sees the increment. The only way to do that
is to make the PTL locks RCsc and that is a much more expensive
proposition.
What about:
CPU0 CPU1
tlb_gather_mmu()
lock PTLn
no mod
unlock PTLn
lock PTLm
mod
include in tlb range
unlock PTLm
tlb_gather_mmu()
lock PTLn
mod
unlock PTLn
tlb_finish_mmu()
force = mm_tlb_flush_nested(tlb->mm);
arch_tlb_finish_mmu(force);
... more ...
tlb_finish_mmu()
Do we want CPU1 to see it here? If so, where does it end?
CPU0 CPU1
tlb_gather_mmu()
lock PTLn
no mod
unlock PTLn
lock PTLm
mod
include in tlb range
unlock PTLm
tlb_finish_mmu()
force = mm_tlb_flush_nested(tlb->mm);
tlb_gather_mmu()
lock PTLn
mod
unlock PTLn
arch_tlb_finish_mmu(force);
... more ...
tlb_finish_mmu()
This?
Could you clarify under what exact condition mm_tlb_flush_nested() must
return true?
next prev parent reply other threads:[~2017-08-13 12:50 UTC|newest]
Thread overview: 112+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-11 7:53 linux-next: manual merge of the akpm-current tree with the tip tree Stephen Rothwell
2017-08-11 9:34 ` Peter Zijlstra
2017-08-11 10:48 ` Peter Zijlstra
2017-08-11 11:45 ` Stephen Rothwell
2017-08-11 11:56 ` Ingo Molnar
2017-08-11 12:17 ` Peter Zijlstra
2017-08-11 12:44 ` Ingo Molnar
2017-08-11 13:49 ` Stephen Rothwell
2017-08-11 14:04 ` Peter Zijlstra
2017-08-13 6:06 ` Nadav Amit
2017-08-13 12:50 ` Peter Zijlstra [this message]
2017-08-14 3:16 ` Minchan Kim
2017-08-14 5:07 ` Nadav Amit
2017-08-14 5:23 ` Minchan Kim
2017-08-14 8:38 ` Minchan Kim
2017-08-14 19:57 ` Peter Zijlstra
2017-08-16 4:14 ` Minchan Kim
2017-08-14 19:38 ` Peter Zijlstra
2017-08-15 7:51 ` Nadav Amit
2017-08-14 3:09 ` Minchan Kim
2017-08-14 18:54 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2022-02-16 5:38 Stephen Rothwell
2021-10-07 6:27 Stephen Rothwell
2021-03-22 6:12 Stephen Rothwell
2020-12-11 8:56 Stephen Rothwell
2020-12-11 12:47 ` Jason Gunthorpe
2020-11-27 7:48 Stephen Rothwell
2020-11-27 7:39 Stephen Rothwell
2020-11-27 11:54 ` Andy Shevchenko
2020-11-30 9:27 ` Thomas Gleixner
2020-11-23 8:05 Stephen Rothwell
2020-11-09 6:00 Stephen Rothwell
2020-10-13 6:59 Stephen Rothwell
2020-07-17 10:19 Stephen Rothwell
2020-05-29 11:05 Stephen Rothwell
2020-05-29 10:18 Stephen Rothwell
2020-05-29 10:05 Stephen Rothwell
2020-05-29 9:58 Stephen Rothwell
2020-05-25 11:04 Stephen Rothwell
2020-05-26 4:41 ` Singh, Balbir
2020-06-03 4:43 ` Stephen Rothwell
2020-05-19 16:18 Stephen Rothwell
2020-03-25 7:48 Stephen Rothwell
2020-03-19 6:42 Stephen Rothwell
2020-01-20 6:37 Stephen Rothwell
2020-01-20 6:30 Stephen Rothwell
2019-10-31 5:43 Stephen Rothwell
2019-06-24 10:24 Stephen Rothwell
2019-05-01 11:10 Stephen Rothwell
2019-01-31 4:31 Stephen Rothwell
2018-08-20 4:32 Stephen Rothwell
2018-08-20 19:52 ` Andrew Morton
2018-03-23 5:59 Stephen Rothwell
2017-12-18 5:04 Stephen Rothwell
2017-11-10 4:33 Stephen Rothwell
2017-11-02 7:19 Stephen Rothwell
2017-08-22 6:57 Stephen Rothwell
2017-08-23 6:39 ` Vlastimil Babka
2017-04-12 6:46 Stephen Rothwell
2017-04-12 20:53 ` Vlastimil Babka
2017-04-20 2:17 ` NeilBrown
2017-03-24 5:25 Stephen Rothwell
2017-02-17 4:40 Stephen Rothwell
2016-11-14 6:08 Stephen Rothwell
2016-07-29 4:14 Stephen Rothwell
2016-06-15 5:23 Stephen Rothwell
2016-06-18 19:39 ` Manfred Spraul
2016-04-29 6:12 Stephen Rothwell
2016-04-29 6:26 ` Ingo Molnar
2016-03-02 5:40 Stephen Rothwell
2016-02-26 5:07 Stephen Rothwell
2016-02-26 21:35 ` Andrew Morton
2016-02-19 4:09 Stephen Rothwell
2016-02-19 15:26 ` Ard Biesheuvel
2015-12-07 8:06 Stephen Rothwell
2015-10-02 4:21 Stephen Rothwell
2015-07-28 6:00 Stephen Rothwell
2015-07-29 17:12 ` Andrea Arcangeli
2015-07-29 17:47 ` Andy Lutomirski
2015-07-29 18:46 ` Thomas Gleixner
2015-07-30 15:38 ` Andrea Arcangeli
2015-07-29 23:06 ` Stephen Rothwell
2015-07-29 23:07 ` Thomas Gleixner
2015-09-07 23:35 ` Stephen Rothwell
2015-09-08 18:11 ` Linus Torvalds
2015-09-08 22:56 ` Stephen Rothwell
2015-09-08 23:03 ` Linus Torvalds
2015-09-08 23:21 ` Andrew Morton
2015-09-16 6:58 ` Geert Uytterhoeven
2015-06-04 12:07 Stephen Rothwell
2015-04-08 8:28 Stephen Rothwell
2015-04-08 8:25 Stephen Rothwell
2014-03-17 9:31 Stephen Rothwell
2014-03-17 9:36 ` Peter Zijlstra
2014-03-19 23:27 ` Andrew Morton
2014-01-14 4:53 Stephen Rothwell
2014-01-14 5:04 ` Davidlohr Bueso
2014-01-14 12:51 ` Peter Zijlstra
2014-01-14 13:17 ` Geert Uytterhoeven
2014-01-14 13:33 ` Peter Zijlstra
2014-01-14 16:19 ` H. Peter Anvin
2014-01-14 15:15 ` H. Peter Anvin
2014-01-14 15:20 ` Geert Uytterhoeven
2014-01-14 15:41 ` Peter Zijlstra
2014-01-14 15:48 ` H. Peter Anvin
2014-01-07 6:00 Stephen Rothwell
2014-01-07 6:34 ` Tang Chen
2013-11-08 7:48 Stephen Rothwell
2013-11-08 18:58 ` Josh Triplett
2013-11-08 23:20 ` Stephen Rothwell
2013-11-09 0:19 ` Josh Triplett
2013-10-30 6:40 Stephen Rothwell
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