Messages in this thread | | | Date | Tue, 25 Mar 2008 08:42:48 -0400 (EDT) | From | "Robert P. J. Day" <> | Subject | Re: [PATCH] RWSEM: Rewrite rwsem.c and rwsem-spinlock.c more simply. |
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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 ========================================================================
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