On Sat, Sep 14, 2013 at 03:23:53PM -0500, Alexander Graf wrote: > > > Am 14.09.2013 um 00:24 schrieb Paul Mackerras <paulus@xxxxxxxxx>: > > > Bootup (F19 guest, 3 runs): > > > > Without the patch: average 20.12 seconds, st. dev. 0.17 seconds > > With the patch: 20.47 seconds, st. dev. 0.19 seconds > > > > Delta: 0.35 seconds, or 1.7%. > > > > time for i in $(seq 1000); do /bin/echo $i >/dev/null; done: > > > > Without the patch: average 7.27 seconds, st. dev. 0.23 seconds > > With the patch: average 7.55 seconds, st. dev. 0.39 seconds > > > > Delta: 0.28 seconds, or 3.8%. > > > > So there appears to be a small effect, of a few percent. > > So in the normal case it slows us down, but allows ksm to be effective. Do we actually want this change then? I was a bit puzzled why there was a measurable slowdown until I remembered that this patch was intended to go along with the patch "powerpc: Implement __get_user_pages_fast()", which Ben took and which is now upstream in Linus' tree (1f7bf028). So, I applied that patch on top of this "Better handling of host-side read-only pages" pages, and did the same measurements. The results were: Bootup (F19 guest, 3 runs): average 20.05 seconds, st. dev. 0.53s 1000 /bin/echo (4 runs): average 7.27 seconds, st. dev. 0.032s So with both patches applied there is no slowdown at all, and KSM works properly. I think we want this patch. Paul. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
