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authorStephane Eranian <eranian@hpl.hp.com>2006-09-26 10:52:28 +0200
committerAndi Kleen <andi@basil.nowhere.org>2006-09-26 10:52:28 +0200
commitd3a4f48d4866b8623ca9adde8ce4e5fde979c132 (patch)
tree04413a1f18c6f49688d6008b583b20a287920a0f /arch/x86_64/kernel/process.c
parent[PATCH] Clean up asm/smp.h includes (diff)
downloadlinux-d3a4f48d4866b8623ca9adde8ce4e5fde979c132.tar.xz
linux-d3a4f48d4866b8623ca9adde8ce4e5fde979c132.zip
[PATCH] x86-64 TIF flags for debug regs and io bitmap in ctxsw
Hello, 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. This patch covers the x86-64 modifications. A patch for i386 follows. Changelog: - add TIF_DEBUG to track when debug registers are active - add TIF_IO_BITMAP to track when I/O bitmap is used - modify __switch_to() to use the new TIF flags <signed-off-by>: eranian@hpl.hp.com Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'arch/x86_64/kernel/process.c')
-rw-r--r--arch/x86_64/kernel/process.c73
1 files changed, 42 insertions, 31 deletions
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index bb6745d13b8f..6e0527635b4c 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -350,6 +350,7 @@ void exit_thread(void)
kfree(t->io_bitmap_ptr);
t->io_bitmap_ptr = NULL;
+ clear_thread_flag(TIF_IO_BITMAP);
/*
* Careful, clear this in the TSS too:
*/
@@ -369,6 +370,7 @@ void flush_thread(void)
if (t->flags & _TIF_IA32)
current_thread_info()->status |= TS_COMPAT;
}
+ t->flags &= ~_TIF_DEBUG;
tsk->thread.debugreg0 = 0;
tsk->thread.debugreg1 = 0;
@@ -461,7 +463,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long rsp,
asm("mov %%es,%0" : "=m" (p->thread.es));
asm("mov %%ds,%0" : "=m" (p->thread.ds));
- if (unlikely(me->thread.io_bitmap_ptr != NULL)) {
+ if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
if (!p->thread.io_bitmap_ptr) {
p->thread.io_bitmap_max = 0;
@@ -469,6 +471,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long rsp,
}
memcpy(p->thread.io_bitmap_ptr, me->thread.io_bitmap_ptr,
IO_BITMAP_BYTES);
+ set_tsk_thread_flag(p, TIF_IO_BITMAP);
}
/*
@@ -498,6 +501,40 @@ out:
*/
#define loaddebug(thread,r) set_debugreg(thread->debugreg ## r, r)
+static inline void __switch_to_xtra(struct task_struct *prev_p,
+ struct task_struct *next_p,
+ struct tss_struct *tss)
+{
+ struct thread_struct *prev, *next;
+
+ prev = &prev_p->thread,
+ next = &next_p->thread;
+
+ if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
+ loaddebug(next, 0);
+ loaddebug(next, 1);
+ loaddebug(next, 2);
+ loaddebug(next, 3);
+ /* no 4 and 5 */
+ loaddebug(next, 6);
+ loaddebug(next, 7);
+ }
+
+ if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
+ /*
+ * Copy the relevant range of the IO bitmap.
+ * Normally this is 128 bytes or less:
+ */
+ memcpy(tss->io_bitmap, next->io_bitmap_ptr,
+ max(prev->io_bitmap_max, next->io_bitmap_max));
+ } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
+ /*
+ * Clear any possible leftover bits:
+ */
+ memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+ }
+}
+
/*
* switch_to(x,y) should switch tasks from x to y.
*
@@ -586,37 +623,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);
/*
- * Now maybe reload the debug registers
+ * Now maybe reload the debug registers and handle I/O bitmaps
*/
- if (unlikely(next->debugreg7)) {
- loaddebug(next, 0);
- loaddebug(next, 1);
- loaddebug(next, 2);
- loaddebug(next, 3);
- /* no 4 and 5 */
- loaddebug(next, 6);
- loaddebug(next, 7);
- }
-
-
- /*
- * Handle the IO bitmap
- */
- if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) {
- if (next->io_bitmap_ptr)
- /*
- * Copy the relevant range of the IO bitmap.
- * Normally this is 128 bytes or less:
- */
- memcpy(tss->io_bitmap, next->io_bitmap_ptr,
- max(prev->io_bitmap_max, next->io_bitmap_max));
- else {
- /*
- * Clear any possible leftover bits:
- */
- memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
- }
- }
+ if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+ || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+ __switch_to_xtra(prev_p, next_p, tss);
return prev_p;
}