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cpuid: cache the maximum size of xsave state 

perf shows that ExtendedStateSize cosumes more than 20% of cpu:

    23.61%    23.61%  [.] pkg/cpuid/cpuid.HostID

PiperOrigin-RevId: 295813263
This commit is contained in:
gVisor bot 2020-02-18 13:49:17 -08:00
parent 906eb6295d
commit a3582de618
1 changed files with 13 additions and 6 deletions
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19
pkg/cpuid/cpuid_x86.go
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@ -725,6 +725,18 @@ func vendorIDFromRegs(bx, cx, dx uint32) string {
return string(bytes)
}
var maxXsaveSize = func() uint32 {
// Leaf 0 of xsaveinfo function returns the size for currently
// enabled xsave features in ebx, the maximum size if all valid
// features are saved with xsave in ecx, and valid XCR0 bits in
// edx:eax.
//
// If xSaveInfo isn't supported, cpuid will not fault but will
// return bogus values.
_, _, maxXsaveSize, _ := HostID(uint32(xSaveInfo), 0)
return maxXsaveSize
}()
// ExtendedStateSize returns the number of bytes needed to save the "extended
// state" for this processor and the boundary it must be aligned to. Extended
// state includes floating point registers, and other cpu state that's not
@ -736,12 +748,7 @@ func vendorIDFromRegs(bx, cx, dx uint32) string {
// about 2.5K worst case, with avx512).
func (fs *FeatureSet) ExtendedStateSize() (size, align uint) {
if fs.UseXsave() {
// Leaf 0 of xsaveinfo function returns the size for currently
// enabled xsave features in ebx, the maximum size if all valid
// features are saved with xsave in ecx, and valid XCR0 bits in
// edx:eax.
_, _, maxSize, _ := HostID(uint32(xSaveInfo), 0)
return uint(maxSize), 64
return uint(maxXsaveSize), 64
}
// If we don't support xsave, we fall back to fxsave, which requires