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From: Suresh Siddha <suresh.b.siddha@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	asit.k.mallick@intel.com
Subject: Re: [patch] x86, tsc: fix SMI induced variation in quick_pit_calibrate()
Date: Mon, 16 Jan 2012 20:06:04 -0800	[thread overview]
Message-ID: <1326773165.16150.35.camel@sbsiddha-desk.sc.intel.com> (raw)
In-Reply-To: <CA+55aFwuwPXatwdJqeW_e_7w_rBELL8HTHqq0FLDiE+xmPm5XQ@mail.gmail.com>

On Mon, 2012-01-16 at 17:30 -0800, Linus Torvalds wrote:
> On Mon, Jan 16, 2012 at 4:52 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Hmm. I get the feeling that we should remove that line entirely.
> 
> Yeah, I really cannot come up with a single good reason to keep that
> line, and suspect that I was a bit loopy when I wrote it.
> 
> So here's the suggested trivially updated patch. Does this work for people?

It does work. But it is taking almost 105 iterations or so to stabilize.
And if I boot the system in power-save mode (lowest p-state), it takes
almost 115 iterations to stabilize (close to the 25msec limit). This is
on the latest gen platform.

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.

thanks,
suresh


  reply	other threads:[~2012-01-17  3:59 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-16 20:15 [patch] x86, tsc: fix SMI induced variation in quick_pit_calibrate() Suresh Siddha
2012-01-17  0:18 ` Linus Torvalds
2012-01-17  0:41   ` Suresh Siddha
2012-01-17  0:52     ` Linus Torvalds
2012-01-17  1:30       ` Linus Torvalds
2012-01-17  4:06         ` Suresh Siddha [this message]
2012-01-17  5:15           ` Linus Torvalds
2012-01-17 23:35             ` Suresh Siddha
2012-01-18  0:25               ` [tip:x86/urgent] x86, tsc: Fix " tip-bot for Linus Torvalds
2012-01-17  2:47 ` [patch] x86, tsc: fix " Yinghai Lu

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