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Date: Fri, 12 Jun 2015 10:42:51 +0200
From: Borislav Petkov <bp@suse.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>, Aaron Lu <aaron.lu@intel.com>,
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        Fengguang Wu <fengguang.wu@intel.com>, Len Brown <lenb@kernel.org>,
        Ken Xue <ken.xue@amd.com>, Huang Rui <ray.huang@amd.com>,
        X86 ML <x86@kernel.org>
Subject: Re: [PATCH v2 3/4] x86, mwaitt: introduce mwaix delay with a
 configurable timer
Message-ID: <20150612084251.GB9257@pd.tnic>
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On Tue, Jun 09, 2015 at 09:46:52AM -0700, Andy Lutomirski wrote:
> I don't like this hack.  The compiler is entirely within is rights to
> poke addr's cacheline (i.e. the stack) between the two instructions.
> I'd suggest either making the thing a full cacheline long or using a
> single asm statement.

How about this:

        /*
         * This should be a memory location in a cache line which is
         * unlikely to be touched by other processors.  The actual
         * content is immaterial as it is not actually modified in any way.
         */
        mwait_ptr = &current_thread_info()->flags;

and then

	__monitor(mwait_ptr, 0, 0);

We already do this in mwait_play_dead().

However, am I even correct in assuming that ->flags won't really be
touched as we're doing delay() and nothing pokes into current anyway?

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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