linux-kernel - Re: [tip:x86/idle] x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers

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Message-ID: <CA+55aFzRUBrMUgFsJ6tfPrH2k_9gEqwUFEHvJZUz6o+Tf4QSoA@mail.gmail.com>
Date:	Fri, 20 Dec 2013 06:25:05 +0900
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Anvin <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Anvin <hpa@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/idle] x86, idle: Use static_cpu_has() for CLFLUSH
 workaround, add barriers

On Fri, Dec 20, 2013 at 6:14 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
>
> So, my thinking was that maybe it's the other way around: the problem
> is with the write not being drained to cache yet.

That is possible. I haven't seen the exact details of the monitor
errata . If it's just about the write buffer and cache interaction,
then I agree that the barrier after the write in
current_set_polling_and_test() is sufficient.  But in the absense of
knowledge, I think we should have it after the read too.

              Linus
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