* Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: > On 03/30/2018 01:32 PM, Thomas Gleixner wrote: > > On Fri, 30 Mar 2018, Dave Hansen wrote: > > > >> On 03/30/2018 05:17 AM, Ingo Molnar wrote: > >>> BTW., the expectation on !PCID Intel hardware would be for global pages to help > >>> even more than the 0.6% and 1.7% you measured on PCID hardware: PCID already > >>> _reduces_ the cost of TLB flushes - so if there's not even PCID then global pages > >>> should help even more. > >>> > >>> In theory at least. Would still be nice to measure it. > >> > >> I did the lseek test on a modern, non-PCID system: > >> > >> No Global pages (baseline): 6077741 lseeks/sec > >> 94 Global pages (this set): 8433111 lseeks/sec > >> +2355370 lseeks/sec (+38.8%) > > > > That's all kernel text, right? What's the result for the case where global > > is only set for all user/kernel shared pages? > > Yes, that's all kernel text (94 global entries). Here's the number with > just the entry data/text set global (88 global entries on this system): > > No Global pages (baseline): 6077741 lseeks/sec > 88 Global Pages (kentry ): 7528609 lseeks/sec (+23.9%) > 94 Global pages (this set): 8433111 lseeks/sec (+38.8%) Very impressive! Please incorporate the performance numbers in patches #9 and #11. There were a couple of valid review comments which need to be addressed as well, but other than that it all looks good to me and I plan to apply the next iteration. In fact I think I'll try to put it into the backporting tree: as PGE was really the pre PTI status quo and thus we should expect few quirks/bugs in this area, plus we still want to share as much core PTI logic with the -stable kernels as possible. The performance plus doesn't hurt either ... after so much lost performance. Thanks, Ingo
