[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 1/6] x86: Add support for STAC/CLAC instructions
>>> On 22.04.14 at 10:46, <feng.wu@xxxxxxxxx> wrote: >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >> >>> On 22.04.14 at 09:41, <feng.wu@xxxxxxxxx> wrote: >> > BTW, from the Linux implementation, I think we don't need to check the >> > 'cr4' >> > for the macros, we just need >> > to check whether the feature exists in the CPU. So is it acceptable to use >> > the original code by eliminating the cr4 check? >> >> That _might_ be acceptable if you bring it down to just the three >> really necessary instructions: BT, JNC, CLAC/STAC. But the "might" >> has to stand - this, after all, remains an addition of a conditional >> branch (and for the performance of STAC/CLAC I haven't seen any >> documentation so far either) to several fast paths, and hence the >> patching alternative can't be discarded as the potentially better one. >> > > Since the alternatives mechanism in Linux is something common and > independent and needs > a bit more efforts to be ported to Xen, can we use the method I mentioned > above > at the current stage. After that I will have a fully think about how to port > the > alternatives mechanism Xen. > > What do you think about this? Generally this would seem acceptable (as long as you give at least a rough estimate on when to expect that second step), but then we have this sad experience with promises by Intel engineers to work on certain things... Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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