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| author | Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> | 2009-04-24 00:26:50 -0700 |
|---|---|---|
| committer | Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> | 2009-05-08 15:55:24 -0700 |
| commit | a789ed5fb6d0256c4177c2cc27e06520ddbe4d4c (patch) | |
| tree | afdbb0c64c15ec522eae260949bfec02df2291b2 /arch/x86/xen/enlighten.c | |
| parent | b80119bb35a49a4e8dbfb9708872adfd5cf38dee (diff) | |
| download | op-kernel-dev-a789ed5fb6d0256c4177c2cc27e06520ddbe4d4c.zip op-kernel-dev-a789ed5fb6d0256c4177c2cc27e06520ddbe4d4c.tar.gz | |
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/enlighten.c')
| -rw-r--r-- | arch/x86/xen/enlighten.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index e9df942..0a1700a 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -658,10 +658,26 @@ static void xen_clts(void) xen_mc_issue(PARAVIRT_LAZY_CPU); } +static DEFINE_PER_CPU(unsigned long, xen_cr0_value); + +static unsigned long xen_read_cr0(void) +{ + unsigned long cr0 = percpu_read(xen_cr0_value); + + if (unlikely(cr0 == 0)) { + cr0 = native_read_cr0(); + percpu_write(xen_cr0_value, cr0); + } + + return cr0; +} + static void xen_write_cr0(unsigned long cr0) { struct multicall_space mcs; + percpu_write(xen_cr0_value, cr0); + /* Only pay attention to cr0.TS; everything else is ignored. */ mcs = xen_mc_entry(0); @@ -847,7 +863,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = { .clts = xen_clts, - .read_cr0 = native_read_cr0, + .read_cr0 = xen_read_cr0, .write_cr0 = xen_write_cr0, .read_cr4 = native_read_cr4, |
