Messages in this thread | | | Subject | Re: [PATCH 00/11] Use global pages with PTI | From | Dave Hansen <> | Date | Wed, 28 Mar 2018 17:17:56 -0700 |
| |
On 03/27/2018 01:07 PM, Ingo Molnar wrote: > * Thomas Gleixner <tglx@linutronix.de> 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.
1. https://ark.intel.com/products/97933/Intel-Atom-Processor-C3955-16M-Cache-up-to-2_40-GHz 2. https://github.com/antonblanchard/will-it-scale/blob/master/tests/lseek1.c
| |