Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756560AbYJHTqd (ORCPT ); Wed, 8 Oct 2008 15:46:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752146AbYJHTqZ (ORCPT ); Wed, 8 Oct 2008 15:46:25 -0400 Received: from kara.rubysoft.com ([64.34.171.174]:36965 "EHLO kara.rubysoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752045AbYJHTqY (ORCPT ); Wed, 8 Oct 2008 15:46:24 -0400 Date: Wed, 8 Oct 2008 13:46:17 -0600 (MDT) From: Jeff Hansen X-X-Sender: ninkid@ren Reply-To: Jeff Hansen To: Chris Snook cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, mingo@elte.hu Subject: Re: x86_32 tsc/pit and hrtimers In-Reply-To: <48ECFEDC.90305@redhat.com> Message-ID: References: <48ECFEDC.90305@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2946 Lines: 70 Chris, This worked perfectly! I second adding a kernel option that forces trusting the TSC. I can make a patch if you'd like. Should the option be something like "trusttsc" or "tsc=noverify"? -Jeff --------------------------------------------------- "If someone's gotta do it, it might as well be me." On Wed, 8 Oct 2008, Chris Snook wrote: > Jeff Hansen wrote: >> Linus, Ingo, All, >> >> I've been struggling with hrtimer support in 2.6.26.5 on an older >> x86_32/i386 system, and I'm wondering if there are any easy fixes that you >> (or anyone else) would suggest. >> >> Basically, this system does not print out the message: >> >> "Switched to high resolution mode on CPU 0" >> >> indicating that one-shot, hrtimers, etc. won't work, since high resolution >> mode has not been enabled. I've verified that hrtimers started with >> hrtimer_start do not have the expected resolution further than 1/HZ. >> >> This system does not have LAPIC, ACPI, or HPET, so really the only >> clocksources I can use are TSC and PIT. This should be fine (in theory, >> unless it wasn't designed like that), but apparently the clocksource flags >> are not initialized in such a way that one of them ever gets marked as >> CLOCK_SOURCE_VALID_FOR_HRES. >> >> The flow of the flags on each of these clocksources is as follows: >> >> 1) The flags on the TSC clocksource are CLOCK_SOURCE_IS_CONTINUOUS | >> CLOCK_SOURCE_MUST_VERIFY, which causes PIT to be used as the watchdog >> clocksource. (see kernel/time/clocksource.c:~171) >> 2) Around line 122 in kernel/time/clocksource.c, where most clocksources' >> flags usually get ORed with CLOCK_SOURCE_VALID_FOR_HRES, the PIT's do >> not because it is not CLOCK_SOURCE_IS_CONTINUOUS, and the TSC's do not >> also because the PIT (as the watchdog) is not >> CLOCK_SOURCE_IS_CONTINUOUS. >> >> I get the same results on a new laptop booting into 32-bit Linux with hpet >> and acpi disabled. >> >> 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? >> >> -Jeff Hansen > > 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? > > -- Chris > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/