From: Max Krasnyansky <maxk@qualcomm.com>
To: Robert Crocombe <rcrocomb@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch] x86: unify/rewrite SMP TSC sync code
Date: Mon, 27 Nov 2006 10:41:20 -0800 [thread overview]
Message-ID: <456B3150.7020705@qualcomm.com> (raw)
In-Reply-To: <e6babb600611270923h139a59ecr82af786f3aedf607@mail.gmail.com>
> Using gtod() can amount to a substantial disturbance of the thing to
> be measured. Using rdtsc, things seem reliable so far, and we have an
> FPGA (accessed through the PCI bus) that has been programmed to give
> access to an 8MHz clock and we do some checks against that.
Same here. gettimeofday() is way too slow (dual Opteron box) for the
frequency I need to call it at. HPET is not available. But TSC is doing just
fine. Plus in my case I don't care about sync between CPUs (thread that uses
TSC is running on the isolated CPU) and I have external time source that takes
care of the drift.
So please no trapping of the RDTSC. Making it clear (bold kernel message during
boot :-) that TSC(s) are not in sync or unstable (from GTOD point of view) is of
course perfectly fine.
Thanx
Max
next prev parent reply other threads:[~2006-11-27 18:41 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-27 17:23 [patch] x86: unify/rewrite SMP TSC sync code Robert Crocombe
2006-11-27 18:41 ` Max Krasnyansky [this message]
[not found] <fa./NRPJg+JjfSQLUVwnX1GpHGIojQ@ifi.uio.no>
[not found] ` <fa.Y0RKABHd+7qnbGQYBAGPvlJ0Qic@ifi.uio.no>
[not found] ` <fa.fD3WSpNqEJ4736vYzEak5Gf3xTw@ifi.uio.no>
[not found] ` <fa.A+gkQAO1DLThaxJxPLPl3yE1CGo@ifi.uio.no>
[not found] ` <fa.INurNKWdUKAEULTHyfpSW65a/Ng@ifi.uio.no>
[not found] ` <fa.n9vySiI9RS2MCl0DZPDzxZEPiFw@ifi.uio.no>
2006-11-26 7:20 ` Robert Hancock
2006-11-26 8:16 ` Wink Saville
2006-11-26 8:24 ` Arjan van de Ven
2006-11-26 19:48 ` Wink Saville
2006-11-27 7:51 ` Arjan van de Ven
2006-11-27 9:15 ` Wink Saville
-- strict thread matches above, loose matches on Subject: below --
2006-11-24 17:02 Ingo Molnar
2006-11-24 17:13 ` Andi Kleen
2006-11-24 20:25 ` Ingo Molnar
2006-11-24 20:37 ` Andi Kleen
2006-11-24 20:46 ` Ingo Molnar
2006-11-24 21:06 ` Andi Kleen
2006-11-24 22:48 ` Ben Greear
2006-11-25 2:56 ` Wink Saville
2006-11-25 8:30 ` Arjan van de Ven
2006-11-25 16:58 ` Wink Saville
2006-11-25 17:41 ` Arjan van de Ven
2006-11-25 20:34 ` Wink Saville
2006-11-27 19:00 ` Christoph Lameter
2006-11-29 7:13 ` Ingo Molnar
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