>>> On 04.04.18 at 08:07, <jgr...@suse.com> wrote: > On 03/04/18 19:48, Juergen Gross wrote: >> On 19/03/18 14:37, Jan Beulich wrote: >>> Introduce a synthetic feature flag to use alternative instruction >>> patching to NOP out all code on entry/exit paths. Having NOPs here is >>> generally better than using conditional branches. >>> >>> Also change the limit on the number of bytes we can patch in one go to >>> that resulting from the encoding in struct alt_instr - there's no point >>> reducing it below that limit, and without a check being in place that >>> the limit isn't actually exceeded, such an artificial boundary is a >>> latent risk. >>> >>> Signed-off-by: Jan Beulich <jbeul...@suse.com> >> >> Just did a parallel make of the hypervisor with and without the patch, >> with xpti=true and with xpti=false (values in braces are stddev). > > The unpatched version was configured differently than the patched one. > So the real numbers are: > > elapsed system user > unpatched, xpti=false: 89.96 ( 8.07) 97.05 ( 5.69) 178.64 ( 2.39) > unpatched, xpti=true : 113.42 ( 9.80) 165.99 (15.10) 180.99 ( 2.66) > patched, xpti=false: 90.65 ( 6.63) 99.50 (14.79) 180.35 ( 5.97) > patched, xpti=true : 111.69 ( 9.93) 163.63 (13.05) 181.22 ( 3.71) > > So the XPTI case is a little bit faster with the patch, while the > non-XPTI case is a little bit slower.
That's rather counterintuitive a result. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
