Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1424260AbWKIXng (ORCPT ); Thu, 9 Nov 2006 18:43:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1424207AbWKIXjj (ORCPT ); Thu, 9 Nov 2006 18:39:39 -0500 Received: from www.osadl.org ([213.239.205.134]:3485 "EHLO mail.tglx.de") by vger.kernel.org with ESMTP id S1161874AbWKIXjO (ORCPT ); Thu, 9 Nov 2006 18:39:14 -0500 Message-Id: <20061109233035.569684000@cruncher.tec.linutronix.de> References: <20061109233030.915859000@cruncher.tec.linutronix.de> Date: Thu, 09 Nov 2006 23:38:30 -0000 From: Thomas Gleixner To: Andrew Morton Cc: LKML , Ingo Molnar , Len Brown , John Stultz , Arjan van de Ven , Andi Kleen , Roman Zippel Subject: [patch 13/19] GTOD: Mark TSC unusable for highres timers Content-Disposition: inline; filename=gtod-mark-tsc-unusable-for-highres-timers.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1941 Lines: 48 From: Thomas Gleixner The TSC is too unstable and unreliable to be used with high resolution timers. The automatic detection of TSC unstability fails once we switched to high resolution mode, because the tick emulation would use the TSC as reference. This results in a circular dependency. Mark it unusable for high res upfront. [akpm@osdl.org: updated for i386-time-avoid-pit-smp-lockups.patch] Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar diff -puN arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers arch/i386/kernel/tsc.c --- a/arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers +++ a/arch/i386/kernel/tsc.c @@ -459,10 +459,23 @@ static int __init init_tsc_clocksource(v current_tsc_khz = tsc_khz; clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz, clocksource_tsc.shift); +#ifndef CONFIG_HIGH_RES_TIMERS /* lower the rating if we already know its unstable: */ if (check_tsc_unstable()) clocksource_tsc.rating = 0; - +#else + /* + * Mark TSC unsuitable for high resolution timers. TSC has so + * many pitfalls: frequency changes, stop in idle ... When we + * switch to high resolution mode we can not longer detect a + * firmware caused frequency change, as the emulated tick uses + * TSC as reference. This results in a circular dependency. + * Switch only to high resolution mode, if pm_timer or such + * is available. + */ + clocksource_tsc.rating = 50; + clocksource_tsc.is_continuous = 0; +#endif init_timer(&verify_tsc_freq_timer); verify_tsc_freq_timer.function = verify_tsc_freq; verify_tsc_freq_timer.expires = _ -- - 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/