ä 10/16/2010 11:03 AM, Koornstra, Reinoud åé:
-----Original Message-----
From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-
owner@xxxxxxxxxxxxxxx] On Behalf Of Rafael J. Wysocki
Sent: Thursday, October 07, 2010 2:44 PM
To: Greg KH
Cc: Sameer Nanda; lenb@xxxxxxxxxx; stefan.bader@xxxxxxxxxxxxx;
brad.figg@xxxxxxxxxxxxx; apw@xxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH] ACPI: Read TSC upon resume
On Thursday, October 07, 2010, Greg KH wrote:
On Thu, Oct 07, 2010 at 11:05:21AM -0700, Sameer Nanda wrote:
On Thu, Oct 7, 2010 at 10:46 AM, Greg KH<gregkh@xxxxxxx> wrote:
On Thu, Oct 07, 2010 at 10:43:34AM -0700, Sameer Nanda wrote:
On Wed, Oct 6, 2010 at 7:19 PM, Greg KH<gregkh@xxxxxxx> wrote:
And are you always going to be printing this out? Why do we
want to
know this every time?
Yes, every time. This helps track variance in BIOS resume times
within a
single boot.
Is that really something that users can do something about?
Aside from complaining to the BIOS vendors, no :)
Then I would not recommend adding this patch, as it is irrelevant for
99.9999% of all Linux users.
It may be somewhat useful, but the rdtscll() call seems to be x86-
specific, in
which case it shouldn't be used at this place.
Also, in the case of an intel core 2 duo cpu, the tsc is not stable, hence upon resume the cpu is spinning up and the first tsc's will be slower.
During idle-time the tsc will not be incremented. The tsc is only stably incremented upon 100% cpu usage. It also doesn't increment faster in turbo mode in case of some core 2 duo and certainly the Nehalem cpu's. Calculating in time in terms of tsc might not be so reliable.
If I'm wrong, please feel free to fix me.
I have 2 questions to your answer:
1. CPU has a flag named constant_tsc to keep TSC always working in a
constant way, so it is irrelvant to the CPU freq. whether in turbo mode
or any P-state CPU currently belongs to, TSC should be not affected.
IIRC, this flag should exist long before, at least before Core 2 duo. If
so, TSC shoule be stable in this kind of environment.
2. though during idle-time TSC will not be incremented, here I want to
remind it is right before Westmere (TSC not always running), and you
mentioned "upon resume the cpu is spinning up and the first tsc's will
be slower", I don't know if this commit cd7240c0b can fix it up.
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