Ingo Molnar wrote: > * Avi Kivity <[EMAIL PROTECTED]> wrote: > > >>> lat_ctx -s 0 [zero memory footprint]: >>> >>> ------------------------------------------------- >>> #tasks native kvm-r4204 kvm-r4232(mmu) >>> ------------------------------------------------- >>> 2: 2.02 180.91 9.19 >>> 20: 4.04 183.21 10.01 >>> 50: 4.30 185.95 11.27 >>> >>> so here it's a /massive/, almost 20 times speedup! >>> >>> >> Excellent. 10us is approximately the vmexit overhead on intel (we >> regularly see 100-120k exits/sec), so it means a context switch is >> exactly one exit. Hard to beat without nested page tables. >> > > actually, the VM entry+exit cost on this CPU is around 3-4 microseconds, > so it's still 2 VM exits per context switch. > > I debugged this a bit, and what happens is that when Linux does a > task-switch it does a cr3 load /and/ a write (look at __flush_tlb()) - > and both are causing a vm exit! > > I have started paravirtualizing the Linux kernel for KVM. I have > eliminated the cr3 load from the Linux kernel via paravirtualization and > that way lat_ctx shows a ~5-6 usecs context-switch cost. That's pretty > good i think, compared to the 2-3 usecs of native. I'll send patches for > this tomorrow. >
Does this really call for parvirtualization? Caching the old cr3 value will work for native as well. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
