On 3/26/22 02:37, Jon Kohler wrote:
Flip the ordering of the || condition so that XFEATURE_MASK_PKRU is
checked first, which when instrumented in our environment appeared
to be always true and less overall work than kvm_read_cr4_bits.
If it's always true, then it should be checked last, not first. And if
Sean thanks for the review. This would be a left handed || short circuit, so
wouldn’t we want always true to be first?
Yes.
Not that it really matters, since static_cpu_has() will patch out all the branches,
and in practice who cares about a JMP or NOP(s)? But...
The reason I’ve been pursuing this is that the guest+host xsave adds up to
a bit over ~1% as measured by perf top in an exit heavy workload. This is
the first in a few patch we’ve drummed up to to get it back towards zero.
I’ll send the rest out next week.
Can you add a testcase to x86/vmexit.c in kvm-unit-tests, too?
Thanks,
Paolo
