aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/xen
diff options
context:
space:
mode:
authorJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>2009-04-24 03:26:50 -0400
committerJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>2009-05-08 18:55:24 -0400
commita789ed5fb6d0256c4177c2cc27e06520ddbe4d4c (patch)
treeafdbb0c64c15ec522eae260949bfec02df2291b2 /arch/x86/xen
parentb80119bb35a49a4e8dbfb9708872adfd5cf38dee (diff)
xen: cache cr0 value to avoid trap'n'emulate for read_cr0
stts() is implemented in terms of read_cr0/write_cr0 to update the state of the TS bit. This happens during context switch, and so is fairly performance critical. Rather than falling back to a trap-and-emulate native read_cr0, implement our own by caching the last-written value from write_cr0 (the TS bit is the only one we really care about). Impact: optimise Xen context switches Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Diffstat (limited to 'arch/x86/xen')
-rw-r--r--arch/x86/xen/enlighten.c18
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index e9df942aa14..0a1700a2be9 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -658,10 +658,26 @@ static void xen_clts(void)
658 xen_mc_issue(PARAVIRT_LAZY_CPU); 658 xen_mc_issue(PARAVIRT_LAZY_CPU);
659} 659}
660 660
661static DEFINE_PER_CPU(unsigned long, xen_cr0_value);
662
663static unsigned long xen_read_cr0(void)
664{
665 unsigned long cr0 = percpu_read(xen_cr0_value);
666
667 if (unlikely(cr0 == 0)) {
668 cr0 = native_read_cr0();
669 percpu_write(xen_cr0_value, cr0);
670 }
671
672 return cr0;
673}
674
661static void xen_write_cr0(unsigned long cr0) 675static void xen_write_cr0(unsigned long cr0)
662{ 676{
663 struct multicall_space mcs; 677 struct multicall_space mcs;
664 678
679 percpu_write(xen_cr0_value, cr0);
680
665 /* Only pay attention to cr0.TS; everything else is 681 /* Only pay attention to cr0.TS; everything else is
666 ignored. */ 682 ignored. */
667 mcs = xen_mc_entry(0); 683 mcs = xen_mc_entry(0);
@@ -847,7 +863,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = {
847 863
848 .clts = xen_clts, 864 .clts = xen_clts,
849 865
850 .read_cr0 = native_read_cr0, 866 .read_cr0 = xen_read_cr0,
851 .write_cr0 = xen_write_cr0, 867 .write_cr0 = xen_write_cr0,
852 868
853 .read_cr4 = native_read_cr4, 869 .read_cr4 = native_read_cr4,