Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755039AbYCYMnB (ORCPT ); Tue, 25 Mar 2008 08:43:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753389AbYCYMmx (ORCPT ); Tue, 25 Mar 2008 08:42:53 -0400 Received: from astoria.ccjclearline.com ([64.235.106.9]:46972 "EHLO astoria.ccjclearline.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753341AbYCYMmw (ORCPT ); Tue, 25 Mar 2008 08:42:52 -0400 Date: Tue, 25 Mar 2008 08:42:48 -0400 (EDT) From: "Robert P. J. Day" X-X-Sender: rpjday@localhost.localdomain To: Andi Kleen cc: Linux Kernel Mailing List , Andrew Morton Subject: Re: [PATCH] RWSEM: Rewrite rwsem.c and rwsem-spinlock.c more simply. In-Reply-To: <20080325123633.GL2170@one.firstfloor.org> Message-ID: References: <87skyfgg4y.fsf@basil.nowhere.org> <20080325123633.GL2170@one.firstfloor.org> User-Agent: Alpine 1.00 (LFD 882 2007-12-20) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - astoria.ccjclearline.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - crashcourse.ca X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5422 Lines: 98 On Tue, 25 Mar 2008, Andi Kleen wrote: > > i'm not sure what this means -- which of the transformations in > > that patch is considered unsafe? here's a typical simplification: > > It is not unsafe, just generates slight worse code. > > current is inline assembler and the compiler doesn't know that it > could cache it in a register because it is not marked pure for > various reasons. That is why current is often cached explicitely in > a local variable to tell the compiler that. ah, i think i see, thanks. learn something every day. > Before you run off and do that everywhere: it is also not a large > win, just a small one unless current is used very often. there's actually not that many explicit calls to either set_task_state or __set_task_state in the entire tree, and a lot of those don't count as they really are setting the state for a different task or for some other reason. in fact, here's the entire list for the whole tree: $ grep -r set_task_state * arch/powerpc/kernel/semaphore.c: __set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/powerpc/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/powerpc/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); arch/powerpc/kernel/semaphore.c: __set_task_state(tsk, TASK_INTERRUPTIBLE); arch/powerpc/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/powerpc/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); arch/alpha/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/alpha/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/parisc/kernel/semaphore.c: set_task_state(current, TASK_UNINTERRUPTIBLE); arch/parisc/kernel/semaphore.c: set_task_state(current, TASK_INTERRUPTIBLE); arch/mn10300/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/mn10300/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/mn10300/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/mn10300/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/s390/kernel/semaphore.c: __set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/s390/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/s390/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); arch/s390/kernel/semaphore.c: __set_task_state(tsk, TASK_INTERRUPTIBLE); arch/s390/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/s390/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); arch/s390/mm/fault.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/s390/mm/fault.c: set_task_state(tsk, TASK_RUNNING); arch/frv/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/frv/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/frv/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/frv/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/mips/kernel/semaphore.c: __set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/mips/kernel/semaphore.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); arch/mips/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); arch/mips/kernel/semaphore.c: __set_task_state(tsk, TASK_INTERRUPTIBLE); arch/mips/kernel/semaphore.c: set_task_state(tsk, TASK_INTERRUPTIBLE); arch/mips/kernel/semaphore.c: __set_task_state(tsk, TASK_RUNNING); Documentation/scheduler/sched-coding.txt:set_task_state(tsk, state_value) drivers/mmc/core/sdio_irq.c: set_task_state(current, TASK_INTERRUPTIBLE); drivers/mmc/core/sdio_irq.c: set_task_state(current, TASK_RUNNING); drivers/mfd/ucb1x00-ts.c: set_task_state(tsk, TASK_INTERRUPTIBLE); drivers/mfd/ucb1x00-ts.c: set_task_state(tsk, TASK_INTERRUPTIBLE); fs/aio.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); fs/aio.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); fs/aio.c: __set_task_state(tsk, TASK_RUNNING); fs/aio.c: set_task_state(tsk, TASK_INTERRUPTIBLE); fs/aio.c: set_task_state(tsk, TASK_RUNNING); include/linux/sched.h:/* Convenience macros for the sake of set_task_state */ include/linux/sched.h:#define __set_task_state(tsk, state_value) \ include/linux/sched.h:#define set_task_state(tsk, state_value) \ kernel/ptrace.c: __set_task_state(child, TASK_STOPPED); kernel/fork.c: __set_task_state(p, TASK_STOPPED); kernel/mutex.c: __set_task_state(task, state); lib/rwsem-spinlock.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); lib/rwsem-spinlock.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); lib/rwsem-spinlock.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); lib/rwsem-spinlock.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); lib/rwsem.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); lib/rwsem.c: set_task_state(tsk, TASK_UNINTERRUPTIBLE); once you ignore the semaphore stuff (and a bit of the rest, like the stuff in sched.h), there's not really that much left that could be rewritten with set_current_state() anyway. rday -- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry: Have classroom, will lecture. http://crashcourse.ca Waterloo, Ontario, CANADA ======================================================================== -- 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/