diff options
| author | Jeremy Fitzhardinge <jeremy@goop.org> | 2009-02-27 13:25:21 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-03-02 12:07:48 +0100 |
| commit | db949bba3c7cf2e664ac12e237c6d4c914f0c69d (patch) | |
| tree | 4de65831dd1de95f642bed15bc9788edd74c48da /arch/x86/include/asm | |
| parent | 645af4e9e0e32481e3336dda813688732c7e5f0f (diff) | |
x86-32: use non-lazy io bitmap context switching
Impact: remove 32-bit optimization to prepare unification
x86-32 and -64 differ in the way they context-switch tasks
with io permission bitmaps. x86-64 simply copies the next
tasks io bitmap into place (if any) on context switch. x86-32
invalidates the bitmap on context switch, so that the next
IO instruction will fault; at that point it installs the
appropriate IO bitmap.
This makes context switching IO-bitmap-using tasks a bit more
less expensive, at the cost of making the next IO instruction
slower due to the extra fault. This tradeoff only makes sense
if IO-bitmap-using processes are relatively common, but they
don't actually use IO instructions very often.
However, in a typical desktop system, the only process likely
to be using IO bitmaps is the X server, and nothing at all on
a server. Therefore the lazy context switch doesn't really win
all that much, and its just a gratuitious difference from
64-bit code.
This patch removes the lazy context switch, with a view to
unifying this code in a later change.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/include/asm')
| -rw-r--r-- | arch/x86/include/asm/processor.h | 6 |
1 files changed, 0 insertions, 6 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index c7a98f738210..76139506c3e4 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -248,7 +248,6 @@ struct x86_hw_tss { #define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long)) #define IO_BITMAP_OFFSET offsetof(struct tss_struct, io_bitmap) #define INVALID_IO_BITMAP_OFFSET 0x8000 -#define INVALID_IO_BITMAP_OFFSET_LAZY 0x9000 struct tss_struct { /* @@ -263,11 +262,6 @@ struct tss_struct { * be within the limit. */ unsigned long io_bitmap[IO_BITMAP_LONGS + 1]; - /* - * Cache the current maximum and the last task that used the bitmap: - */ - unsigned long io_bitmap_max; - struct thread_struct *io_bitmap_owner; /* * .. and then another 0x100 bytes for the emergency kernel stack: |