linux-kernel - Re: x86_32 tsc/pit and hrtimers

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Message-ID: <20081009172009.GD1370@ucw.cz>
Date:	Thu, 9 Oct 2008 19:20:09 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Chris Snook <csnook@...hat.com>
Cc:	Jeff Hansen <x@...fhansen.com>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: x86_32 tsc/pit and hrtimers

Hi!

>> Can you please tell me if this is supposed to work, and I just have a
>> poorly configured kernel; or if TSC/PIT drivers were not designed to work
>> this way in the first place.  If it wasn't designed to do this, do you
>> have any tips on implementing this, since I'll be needing to do that?
>>
> This is not supposed to work, but it might be worthwhile to add a boot 
> option to force the kernel to trust the TSC, as hardware that lacks any 
> high-res timers also tends to be primitive enough that the TSC can be 
> trusted, if it exists.  If you patch out the CLOCK_SOURCE_MUST_VERIFY 
> flag on the TSC, do you get correctly-functioning high-res timers on this 
> system?

Untrue. Unstable tsc dates back to pentium MMX times.

-- 
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