Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759897AbXFRIbd (ORCPT ); Mon, 18 Jun 2007 04:31:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754227AbXFRIbZ (ORCPT ); Mon, 18 Jun 2007 04:31:25 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:51558 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752391AbXFRIbY (ORCPT ); Mon, 18 Jun 2007 04:31:24 -0400 Date: Mon, 18 Jun 2007 10:31:09 +0200 From: Ingo Molnar To: Miklos Szeredi Cc: cebbert@redhat.com, chris@atlee.ca, linux-kernel@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, Ravikiran G Thirumalai Subject: Re: [BUG] long freezes on thinkpad t60 Message-ID: <20070618083109.GA23572@elte.hu> References: <20070524210153.GB19672@elte.hu> <20070616103707.GA28096@elte.hu> <20070618064343.GA31113@elte.hu> <20070618081204.GA11153@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.0.3 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4293 Lines: 133 (Ravikiran Cc:-ed too) * Miklos Szeredi wrote: > > To test this theory, could you try the patch below, does this fix > > your hangs too? > > Not tried yet, but obviously it does, since it's a superset of the > previous fix. I could try without the smb_mb(), but see below. oops - the 64-bit processor.h bits were included by accident - updated patch below. > > This change causes the memory access of the "easy" spin-loop portion > > to be more agressive: after the REP; NOP we'd not do the 'easy-loop' > > with a simple CMPB, but we'd re-attempt the atomic op. > > It looks as if this is going to overflow of the lock counter, no? hm, what do you mean? There's no lock counter. Ingo --------------------------> Subject: [patch] x86: fix spin-loop starvation bug From: Ingo Molnar Miklos Szeredi reported very long pauses (several seconds, sometimes more) on his T60 (with a Core2Duo) which he managed to track down to wait_task_inactive()'s open-coded busy-loop. He observed that an interrupt on one core tries to acquire the runqueue-lock but does not succeed in doing so for a very long time - while wait_task_inactive() on the other core loops waiting for the first core to deschedule a task (which it wont do while spinning in an interrupt handler). The problem is: both the spin_lock() code and the wait_task_inactive() loop uses cpu_relax()/rep_nop(), so in theory the CPU should have guaranteed MESI-fairness to the two cores - but that didnt happen: one of the cores was able to monopolize the cacheline that holds the runqueue lock, for extended periods of time. This patch changes the spin-loop to assert an atomic op after every REP NOP instance - this will cause the CPU to express its "MESI interest" in that cacheline after every REP NOP. Signed-off-by: Ingo Molnar --- include/asm-i386/spinlock.h | 16 ++++------------ include/asm-x86_64/spinlock.h | 15 +++------------ 2 files changed, 7 insertions(+), 24 deletions(-) Index: linux-cfs-2.6.22-rc5.q/include/asm-i386/spinlock.h =================================================================== --- linux-cfs-2.6.22-rc5.q.orig/include/asm-i386/spinlock.h +++ linux-cfs-2.6.22-rc5.q/include/asm-i386/spinlock.h @@ -37,10 +37,7 @@ static inline void __raw_spin_lock(raw_s asm volatile("\n1:\t" LOCK_PREFIX " ; decb %0\n\t" "jns 3f\n" - "2:\t" - "rep;nop\n\t" - "cmpb $0,%0\n\t" - "jle 2b\n\t" + "rep; nop\n\t" "jmp 1b\n" "3:\n\t" : "+m" (lock->slock) : : "memory"); @@ -65,21 +62,16 @@ static inline void __raw_spin_lock_flags "testl $0x200, %[flags]\n\t" "jz 4f\n\t" STI_STRING "\n" - "3:\t" - "rep;nop\n\t" - "cmpb $0, %[slock]\n\t" - "jle 3b\n\t" + "rep; nop\n\t" CLI_STRING "\n\t" "jmp 1b\n" "4:\t" - "rep;nop\n\t" - "cmpb $0, %[slock]\n\t" - "jg 1b\n\t" + "rep; nop\n\t" "jmp 4b\n" "5:\n\t" : [slock] "+m" (lock->slock) : [flags] "r" (flags) - CLI_STI_INPUT_ARGS + CLI_STI_INPUT_ARGS : "memory" CLI_STI_CLOBBERS); } #endif Index: linux-cfs-2.6.22-rc5.q/include/asm-x86_64/spinlock.h =================================================================== --- linux-cfs-2.6.22-rc5.q.orig/include/asm-x86_64/spinlock.h +++ linux-cfs-2.6.22-rc5.q/include/asm-x86_64/spinlock.h @@ -28,10 +28,7 @@ static inline void __raw_spin_lock(raw_s "\n1:\t" LOCK_PREFIX " ; decl %0\n\t" "jns 2f\n" - "3:\n" - "rep;nop\n\t" - "cmpl $0,%0\n\t" - "jle 3b\n\t" + "rep; nop\n\t" "jmp 1b\n" "2:\t" : "=m" (lock->slock) : : "memory"); } @@ -49,16 +46,10 @@ static inline void __raw_spin_lock_flags "testl $0x200, %1\n\t" /* interrupts were disabled? */ "jz 4f\n\t" "sti\n" - "3:\t" - "rep;nop\n\t" - "cmpl $0, %0\n\t" - "jle 3b\n\t" + "rep; nop\n\t" "cli\n\t" "jmp 1b\n" - "4:\t" - "rep;nop\n\t" - "cmpl $0, %0\n\t" - "jg 1b\n\t" + "rep; nop\n\t" "jmp 4b\n" "5:\n\t" : "+m" (lock->slock) : "r" ((unsigned)flags) : "memory"); - 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/