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authorArjan van de Ven <arjan@linux.intel.com>2006-09-26 04:52:36 -0400
committerAndi Kleen <andi@basil.nowhere.org>2006-09-26 04:52:36 -0400
commite07e23e1fd3000289fc7ccc6c71879070d3b19e0 (patch)
tree1290385cacd89e39b7bc1b12b7515b68423d78d3 /arch/x86_64/kernel/traps.c
parent73fea175303926055440c06bc8894f0c5c58afc8 (diff)
[PATCH] non lazy "sleazy" fpu implementation
Right now the kernel on x86-64 has a 100% lazy fpu behavior: after *every* context switch a trap is taken for the first FPU use to restore the FPU context lazily. This is of course great for applications that have very sporadic or no FPU use (since then you avoid doing the expensive save/restore all the time). However for very frequent FPU users... you take an extra trap every context switch. The patch below adds a simple heuristic to this code: After 5 consecutive context switches of FPU use, the lazy behavior is disabled and the context gets restored every context switch. If the app indeed uses the FPU, the trap is avoided. (the chance of the 6th time slice using FPU after the previous 5 having done so are quite high obviously). After 256 switches, this is reset and lazy behavior is returned (until there are 5 consecutive ones again). The reason for this is to give apps that do longer bursts of FPU use still the lazy behavior back after some time. [akpm@osdl.org: place new task_struct field next to jit_keyring to save space] Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Andi Kleen <ak@suse.de> Cc: Andi Kleen <ak@muc.de> Signed-off-by: Andrew Morton <akpm@osdl.org>
Diffstat (limited to 'arch/x86_64/kernel/traps.c')
-rw-r--r--arch/x86_64/kernel/traps.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 28e53342f29..ffc40cff1e0 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -1136,6 +1136,7 @@ asmlinkage void math_state_restore(void)
1136 init_fpu(me); 1136 init_fpu(me);
1137 restore_fpu_checking(&me->thread.i387.fxsave); 1137 restore_fpu_checking(&me->thread.i387.fxsave);
1138 task_thread_info(me)->status |= TS_USEDFPU; 1138 task_thread_info(me)->status |= TS_USEDFPU;
1139 me->fpu_counter++;
1139} 1140}
1140 1141
1141void __init trap_init(void) 1142void __init trap_init(void)