Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755513AbYGYJCS (ORCPT ); Fri, 25 Jul 2008 05:02:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752905AbYGYJCG (ORCPT ); Fri, 25 Jul 2008 05:02:06 -0400 Received: from dgate20.fujitsu-siemens.com ([80.70.172.51]:27274 "EHLO dgate20.fujitsu-siemens.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752687AbYGYJCF (ORCPT ); Fri, 25 Jul 2008 05:02:05 -0400 DomainKey-Signature: s=s768; d=fujitsu-siemens.com; c=nofws; q=dns; h=X-SBRSScore:X-IronPort-AV:Received:X-IronPort-AV: Received:Received:Message-ID:Date:From:Organization: User-Agent:MIME-Version:To:CC:Subject:References: In-Reply-To:Content-Type; b=MbR0k9zfRPLIx9pACgrLIJ0K+C6nvuDWVw7Bq/XqXSghF9F5UB7OH1UW ooFqQszmA429txh+n8aRM7kHteeV0Af9OfmBvHTiQeZvEVZsuN3ouXwcS COW8UlXHAcf3OXs; X-SBRSScore: None X-IronPort-AV: E=Sophos;i="4.31,252,1215381600"; d="diff'?scan'208";a="21177649" X-IronPort-AV: E=Sophos;i="4.31,251,1215381600"; d="diff'?scan'208";a="32935004" Message-ID: <4889968E.6020000@fujitsu-siemens.com> Date: Fri, 25 Jul 2008 11:02:06 +0200 From: Martin Wilck Organization: Fujitsu Siemens Computers User-Agent: Thunderbird 2.0.0.15pre (X11/20080508) MIME-Version: 1.0 To: Martin Wilck CC: Cyrill Gorcunov , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "H. Peter Anvin" , "Wichert, Gerhard" , "Maciej W. Rozycki" Subject: Re: [PATCH] x86 (64): make calibrate_APIC_clock() SMI-safe (take 2) References: <48885DDC.9010003@fujitsu-siemens.com> <20080724111631.GA3432@lenovo> <48886E6D.1030005@fujitsu-siemens.com> <20080724120512.GA21804@lenovo> <488889B6.9070707@fujitsu-siemens.com> <20080724143151.GA32422@lenovo> <20080724150116.GC32422@lenovo> <48889C14.4070408@fujitsu-siemens.com> In-Reply-To: <48889C14.4070408@fujitsu-siemens.com> Content-Type: multipart/mixed; boundary="------------080705040003040700010305" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4632 Lines: 140 This is a multi-part message in MIME format. --------------080705040003040700010305 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit I wrote: > This patch fixes this by two separate measures: > a) make sure that no significant interruption occurs between APIC and > TSC reads > b) make sure that the measurement loop isn't significantly longer > than originally intended. Here is a new, simplified version of our patch that only uses measure a). We verified that this is sufficient for accurate calibration. If we fail to determine the start or end time of the calibration correctly 10 times in a row, we will print a critical error message and go on. One might as well argue that this should cause a kernel panic (it is impossible to run on the CPU for only a few cycles without being interrupted by an SMI!), but Cyrill probably won't agree. Martin -- Martin Wilck PRIMERGY System Software Engineer FSC IP ESP DEV 6 Fujitsu Siemens Computers GmbH Heinz-Nixdorf-Ring 1 33106 Paderborn Germany Tel: ++49 5251 8 15113 Fax: ++49 5251 8 20209 Email: mailto:martin.wilck@fujitsu-siemens.com Internet: http://www.fujitsu-siemens.com Company Details: http://www.fujitsu-siemens.com/imprint.html --------------080705040003040700010305 Content-Type: text/x-patch; name="calibrate_APIC_clock-4.diff" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="calibrate_APIC_clock-4.diff" [PATCH] x86 (64): make calibrate_APIC_clock() SMI-safe (take 2) Non-maskable asynchronous events (e.g. SMIs) which occur during the APIC timer calibration can cause timer miscalibrations, sometimes by large amounts. This patch fixes this by making sure that no significant interruption occurs between APIC and TSC reads. SMIs may still occur at some stage in the calibration loop, causing the loop to last longer than intended. This doesn't matter though, as long as the start and end values are both taken simultaneously. Signed-off-by: Martin Wilck Signed-off-by: Gerhard Wichert --- arch/x86/kernel/apic_64.c 2008-07-25 10:45:09.000000000 +0200 +++ arch/x86/kernel/apic_64.c.new 2008-07-25 10:45:19.000000000 +0200 @@ -300,6 +300,31 @@ static void setup_APIC_timer(void) } /* + * Helper function for calibrate_APIC_clock(): Make sure that + * APIC TMCTT and TSC are read at the same time, to reasonable + * accuracy. On any sane system, the retry loop won't need more + * than a single retry, given that the rdtsc/apic_read/rdtsc + * sequence won't take more than a few cycles. + */ + +#define MAX_DIFFERENCE 1000UL +#define MAX_ITER 10 +static inline int +__read_tsc_and_apic(unsigned long *tsc, unsigned *apic) +{ + unsigned long tsc0, tsc1, diff; + int i = 0; + do { + rdtscll(tsc0); + *apic = apic_read(APIC_TMCCT); + rdtscll(tsc1); + diff = tsc1 - tsc0; + } while (diff > MAX_DIFFERENCE && ++i < MAX_ITER); + *tsc = tsc0 + (diff >> 1); + return diff > MAX_DIFFERENCE ? -EIO : 0; +} + +/* * In this function we calibrate APIC bus clocks to the external * timer. Unfortunately we cannot use jiffies and the timer irq * to calibrate, since some later bootup code depends on getting @@ -318,7 +343,7 @@ static void __init calibrate_APIC_clock( { unsigned apic, apic_start; unsigned long tsc, tsc_start; - int result; + int result, err_start, err; local_irq_disable(); @@ -331,23 +356,25 @@ static void __init calibrate_APIC_clock( */ __setup_APIC_LVTT(250000000, 0, 0); - apic_start = apic_read(APIC_TMCCT); #ifdef CONFIG_X86_PM_TIMER if (apic_calibrate_pmtmr && pmtmr_ioport) { + apic_start = apic_read(APIC_TMCCT); pmtimer_wait(5000); /* 5ms wait */ apic = apic_read(APIC_TMCCT); result = (apic_start - apic) * 1000L / 5; } else #endif { - rdtscll(tsc_start); + err_start = __read_tsc_and_apic(&tsc_start, &apic_start); do { - apic = apic_read(APIC_TMCCT); - rdtscll(tsc); + err = __read_tsc_and_apic(&tsc, &apic); } while ((tsc - tsc_start) < TICK_COUNT && (apic_start - apic) < TICK_COUNT); + if (err_start || err) + printk(KERN_CRIT "calibrate_APIC_clock: SMI flood - " + "the APIC timer calibration may be wrong!\n"); result = (apic_start - apic) * 1000L * tsc_khz / (tsc - tsc_start); } --------------080705040003040700010305-- -- 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/