On 09/04/18 10:28, Jan Beulich wrote: >>>> 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.
OTOH the standard deviation is not really small, so it might be the performance difference is just below noise level. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
