* Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: > On 03/27/2018 01:07 PM, Ingo Molnar wrote: > > * Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >>> systems. Atoms are going to be the easiest thing to get my hands on, > >>> but I tend to shy away from them for performance work. > >> What I have in mind is that I wonder whether the whole circus is worth it > >> when there is no performance advantage on PCID systems. > > I was waiting on trying to find a relatively recent Atom system (they > actually come in reasonably sized servers [1]), but I'm hitting a snag > there, so I figured I'd just share a kernel compile using Ingo's > perf-based methodology on a Skylake desktop system with PCIDs. > > Here's the kernel compile: > > No Global pages (baseline): 186.951 seconds time elapsed ( +- 0.35% ) > 28 Global pages (this set): 185.756 seconds time elapsed ( +- 0.09% ) > -1.195 seconds (-0.64%) > > Lower is better here, obviously. > > I also re-checked everything using will-it-scale's llseek1 test[2] which > is basically a microbenchmark of a halfway reasonable syscall. Higher > here is better. > > No Global pages (baseline): 15783951 lseeks/sec > 28 Global pages (this set): 16054688 lseeks/sec > +270737 lseeks/sec (+1.71%) > > So, both the kernel compile and the microbenchmark got measurably faster. Ok, cool, this is much better! Mind re-sending the patch-set against latest -tip so it can be merged? At this point !PCID Intel hardware is not a primary concern, if something bad happens on them with global pages we can quirk global pages off on them in some way, or so. Thanks, Ingo
