linux-kernel - Re: [patch] x86, tsc: fix SMI induced variation in quick_pit

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Message-ID: <CA+55aFxjzr3qugZdfsPGPw8RooTCzTr4XQubcqjvF=t+GLHE0Q@mail.gmail.com>
Date:	Mon, 16 Jan 2012 21:15:54 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	asit.k.mallick@...el.com
Subject: Re: [patch] x86, tsc: fix SMI induced variation in quick_pit_calibrate()

On Mon, Jan 16, 2012 at 8:06 PM, Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
>
> So I suspect we can either go back to 500ppm error tolerance:
>
>                        if ((d1+d2) >= delta >> 10)
>                                continue;
>
> or increase the MAX_QUICK_PIT_MS bit more.

Agreed. Either works for me. I think I'd prefer increasing
MAX_QUICK_PIT_MS, because 25ms is still a fairly short time, but the
better we can make the precision of the clock, the better off we'll be
later.

So let's just double MAX_QUICK_PIT_MS to 50, ok?

And since you've tested it, I'm perfectly happy to sign off on that
patch so you can add my signed-off-by line. And if you can write a
reasonable description for it, maybe we can get Ingo & co to apply it.

              Linus
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