>>> On 17.12.15 at 10:18, <huaitong....@intel.com> wrote: > On Wed, 2015-12-16 at 02:12 -0700, Jan Beulich wrote: >> > > > On 16.12.15 at 10:03, <huaitong....@intel.com> wrote: >> > On Wed, 2015-12-16 at 01:32 -0700, Jan Beulich wrote: >> > > Depending on how frequently this might get called, the allocation >> > > overhead may not be tolerable. I.e. you may want to set up e.g. >> > > a per-CPU buffer up front. Or you check whether using RDPKRU >> > > (with temporarily setting CR4.PKE) is cheaper than what you >> > > do right now. >> > RDPKRU does cost less than the function, and if temporarily setting >> > CR4.PKE is accepted, I will use RDPKRU instead of the function. >> >> The question isn't just the RDPKRU cost, but that of the two CR4 >> writes. > Testing result with NOW() function: > Time of the function 10 times execution > (XEN)xsave time is 1376 ns > (XEN)read_pkru time is 28 ns
Wow, that's a huge difference. I'm having trouble to believe two CR4 writes are this fast, and an XSAVE of just a single 32-bit item is this slow. But well - you measured it. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
