Messages in this thread Patch in this message | | | Date | Tue, 4 Jul 2006 17:19:02 -0400 | From | Chuck Ebbert <> | Subject | Re: [PATCH 2/2] i386 TIF flags for debug regs and io bitmap in ctxsw |
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In-Reply-To: <20060704072939.GC5902@frankl.hpl.hp.com>
On Tue, 4 Jul 2006 00:29:39 -0700, Stephane Eranian wrote:
> Following my discussion with Andi. Here is a patch that introduces > two new TIF flags to simplify the context switch code in __switch_to(). > The idea is to minimize the number of cache lines accessed in the common > case, i.e., when neither the debug registers nor the I/O bitmap are used.
I get a 5-10% speedup in task switch times with this patch. Some very minor comments:
> <signed-off-by>: eranian@hpl.hp.com
Should be: Signed-off-by: Stephane Eranian <eranian@hpl.hp.com>
> + if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP) == 0) {
preferred:
if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> @@ -674,18 +692,9 @@ struct task_struct fastcall * __switch_t > /* > * Now maybe reload the debug registers > */
/* * Now maybe reload the debug registers and/or IO bitmap */
And this should be added to the patch:
--- 2.6.17-nb.orig/arch/i386/kernel/process.c +++ 2.6.17-nb/arch/i386/kernel/process.c @@ -360,13 +360,12 @@ EXPORT_SYMBOL(kernel_thread); */ void exit_thread(void) { - struct task_struct *tsk = current; - struct thread_struct *t = &tsk->thread; - /* The process may have allocated an io port bitmap... nuke it. */ - if (unlikely(NULL != t->io_bitmap_ptr)) { + if (unlikely(test_thread_flag(TIF_IO_BITMAP))) { int cpu = get_cpu(); struct tss_struct *tss = &per_cpu(init_tss, cpu); + struct task_struct *tsk = current; + struct thread_struct *t = &tsk->thread; kfree(t->io_bitmap_ptr); t->io_bitmap_ptr = NULL; -- Chuck "You can't read a newspaper if you can't read." --George W. Bush - 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/
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