linux-kernel - Re: Q: schedule() and implied barriers on arm64

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Message-ID: <20151019070604.GA17855@gmail.com>
Date:	Mon, 19 Oct 2015 09:06:05 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Q: schedule() and implied barriers on arm64


* Peter Zijlstra <peterz@...radead.org> wrote:

> In any case, its all moot now, since Paul no longer requires schedule() to imply 
> a full barrier.
>
> [...]

Nevertheless from a least-surprise POV it might be worth guaranteeing it, because 
I bet there's tons of code that assumes that schedule() is a heavy operation and 
it's such an easy mistake to make. Since we are so close to having that guarantee, 
we might as well codify it?

Just like system calls are assumed to be barriers in general - and system calls 
are more lightweight than schedule() ...

Thanks,

	Ingo
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