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authorJeremy Fitzhardinge <jeremy@goop.org>2009-02-27 13:25:21 -0800
committerIngo Molnar <mingo@elte.hu>2009-03-02 12:07:48 +0100
commitdb949bba3c7cf2e664ac12e237c6d4c914f0c69d (patch)
tree4de65831dd1de95f642bed15bc9788edd74c48da /arch/x86/kernel/ioport.c
parent645af4e9e0e32481e3336dda813688732c7e5f0f (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/kernel/ioport.c')
-rw-r--r--arch/x86/kernel/ioport.c11
1 files changed, 0 insertions, 11 deletions
diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index e41980a373ab..99c4d308f16b 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -85,19 +85,8 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
t->io_bitmap_max = bytes;
-#ifdef CONFIG_X86_32
- /*
- * Sets the lazy trigger so that the next I/O operation will
- * reload the correct bitmap.
- * Reset the owner so that a process switch will not set
- * tss->io_bitmap_base to IO_BITMAP_OFFSET.
- */
- tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
- tss->io_bitmap_owner = NULL;
-#else
/* Update the TSS: */
memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
-#endif
put_cpu();