From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760708AbZEBUZQ (ORCPT ); Sat, 2 May 2009 16:25:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759715AbZEBUY5 (ORCPT ); Sat, 2 May 2009 16:24:57 -0400 Received: from www.tglx.de ([62.245.132.106]:39591 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759259AbZEBUY4 (ORCPT ); Sat, 2 May 2009 16:24:56 -0400 Message-Id: <20090502202317.506137353@linutronix.de> User-Agent: quilt/0.47-1 Date: Sat, 02 May 2009 20:23:51 -0000 From: Thomas Gleixner To: LKML Cc: Andrew Morton , Ingo Molnar , Tony Luck , Trond Myklebust Subject: [patch] remove put_cpu_no_resched() [ Resend ] References: <20090502202312.124351431@linutronix.de> Content-Disposition: inline; filename=remove-put-cpu-no-resched.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Impact: remove a high latency source put_cpu_no_resched() is an optimization of put_cpu() which unfortunately can cause high latencies. The nfs iostats code uses put_cpu_no_resched() in a code sequence where a reschedule request caused by an interrupt between the get_cpu() and the put_cpu_no_resched() can delay the reschedule for at least HZ. The other users of put_cpu_no_resched() optimize correctly in interrupt code, but there is no real harm in using the put_cpu() function which is an alias for preempt_enable(). The extra check of the preemmpt count is not as critical as the potential source of missing a reschedule. Debugged in the preempt-rt tree and verified in mainline. Signed-off-by: Thomas Gleixner Cc: Ingo Molnar Cc: Tony Luck Cc: Trond Myklebust --- arch/ia64/kernel/perfmon.c | 2 +- fs/nfs/iostat.h | 4 ++-- include/linux/smp.h | 1 - 3 files changed, 3 insertions(+), 4 deletions(-) Index: linux-2.6/arch/ia64/kernel/perfmon.c =================================================================== --- linux-2.6.orig/arch/ia64/kernel/perfmon.c +++ linux-2.6/arch/ia64/kernel/perfmon.c @@ -5595,7 +5595,7 @@ pfm_interrupt_handler(int irq, void *arg (*pfm_alt_intr_handler->handler)(irq, arg, regs); } - put_cpu_no_resched(); + put_cpu(); return IRQ_HANDLED; } Index: linux-2.6/fs/nfs/iostat.h =================================================================== --- linux-2.6.orig/fs/nfs/iostat.h +++ linux-2.6/fs/nfs/iostat.h @@ -31,7 +31,7 @@ static inline void nfs_inc_server_stats( cpu = get_cpu(); iostats = per_cpu_ptr(server->io_stats, cpu); iostats->events[stat]++; - put_cpu_no_resched(); + put_cpu(); } static inline void nfs_inc_stats(const struct inode *inode, @@ -50,7 +50,7 @@ static inline void nfs_add_server_stats( cpu = get_cpu(); iostats = per_cpu_ptr(server->io_stats, cpu); iostats->bytes[stat] += addend; - put_cpu_no_resched(); + put_cpu(); } static inline void nfs_add_stats(const struct inode *inode, Index: linux-2.6/include/linux/smp.h =================================================================== --- linux-2.6.orig/include/linux/smp.h +++ linux-2.6/include/linux/smp.h @@ -177,7 +177,6 @@ static inline void init_call_single_data #define get_cpu() ({ preempt_disable(); smp_processor_id(); }) #define put_cpu() preempt_enable() -#define put_cpu_no_resched() preempt_enable_no_resched() /* * Callback to arch code if there's nosmp or maxcpus=0 on the