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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: huangpei@loongson.cn, Paul Burton <paul.burton@mips.com>,
	"stern@rowland.harvard.edu" <stern@rowland.harvard.edu>,
	"akiyks@gmail.com" <akiyks@gmail.com>,
	"andrea.parri@amarulasolutions.com" 
	<andrea.parri@amarulasolutions.com>,
	"boqun.feng@gmail.com" <boqun.feng@gmail.com>,
	"dlustig@nvidia.com" <dlustig@nvidia.com>,
	"dhowells@redhat.com" <dhowells@redhat.com>,
	"j.alglave@ucl.ac.uk" <j.alglave@ucl.ac.uk>,
	"luc.maranget@inria.fr" <luc.maranget@inria.fr>,
	"npiggin@gmail.com" <npiggin@gmail.com>,
	"paulmck@linux.ibm.com" <paulmck@linux.ibm.com>,
	"will.deacon@arm.com" <will.deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Huacai Chen <chenhc@lemote.com>
Subject: Re: Re: [RFC][PATCH 2/5] mips/atomic: Fix loongson_llsc_mb() wreckage
Date: Tue, 14 May 2019 10:07:53 -0700	[thread overview]
Message-ID: <CAHk-=wgo_NxNYBSfSSGUV=CJPsz6nm_H6UnwsArBb-9GZ_sY_g@mail.gmail.com> (raw)
In-Reply-To: <20190514165614.GV2623@hirez.programming.kicks-ass.net>

On Tue, May 14, 2019 at 9:56 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> Understood; the problem is that "*p++" is not good enough for local_t
> either (on load-store architectures), since it needs to be "atomic" wrt
> all other instructions on that CPU, most notably exceptions.

Right. But I don't think that's the issue here, since if it was then
it would be a problem even on UP.

And while the CPU-local ones want atomicity, they *shouldn't* have the
issue of another CPU modifying them, so even if you were to lose
exclusive ownership of the cacheline (because some other CPU is
reading your per-cpu data for statistics of whatever), the final end
result should be fine.

End result: I suspect ll/sc still works for cpu-local stuff without
any extra loongson hacks.

But I agree that it would be good to verify.

               Linus

  reply	other threads:[~2019-05-14 17:08 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-24 12:36 [RFC][PATCH 0/5] atomic: Fixes to smp_mb__{before,after}_atomic() and mips Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 1/5] mips/atomic: Fix cmpxchg64 barriers Peter Zijlstra
2019-04-24 21:00   ` Paul Burton
2019-04-25  6:59     ` Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 2/5] mips/atomic: Fix loongson_llsc_mb() wreckage Peter Zijlstra
2019-04-24 12:59   ` Peter Zijlstra
2019-04-24 21:18   ` Paul Burton
2019-04-25  4:58     ` huangpei
2019-04-25  7:33       ` Peter Zijlstra
2019-04-25  9:09         ` Peter Zijlstra
2019-04-25 12:14           ` huangpei
2019-04-25  9:12         ` Peter Zijlstra
2019-05-14 15:58           ` Peter Zijlstra
2019-05-14 16:10             ` Linus Torvalds
2019-05-14 16:56               ` Peter Zijlstra
2019-05-14 17:07                 ` Linus Torvalds [this message]
2019-05-15 13:50               ` huangpei
2019-04-25 11:32         ` huangpei
2019-04-25 12:26           ` Peter Zijlstra
2019-04-25 12:51             ` huangpei
2019-04-25 13:31               ` Peter Zijlstra
2019-04-26  2:57                 ` huangpei
2019-05-14 15:46                   ` Peter Zijlstra
2019-04-25 16:12       ` Linus Torvalds
2019-04-25  7:15     ` Peter Zijlstra
2019-04-24 12:36 ` [RFC][PATCH 3/5] mips/atomic: Optimize loongson3_llsc_mb() Peter Zijlstra
2019-04-24 12:37 ` [RFC][PATCH 4/5] mips/atomic: Fix smp_mb__{before,after}_atomic() Peter Zijlstra
2019-04-24 21:24   ` Paul Burton
2019-04-25  7:34     ` Peter Zijlstra
2019-04-24 12:37 ` [RFC][PATCH 5/5] x86/atomic: " Peter Zijlstra
2019-04-24 13:41   ` Will Deacon

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