[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: Poor performance on HVM (kernbench)
On Thu, Sep 11, 2008 at 2:26 PM, Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx> wrote: > George Dunlap wrote: >> >> So, the problem appears to be with a ton of brute-force searches to >> remove writable mappings, both during resync and promotion. My >> analysis tool is reporting that of the 30 seconds or so in the trace >> from xen-unstable, the guest spent a whopping 67% in the hypervisor: >> * 26% doing resyncs as a result of marking another page out-of-sync >> * 9% promoting pages >> * 27% resyncing as a result of cr3 switches >> And almost the entirety of all of those can be attributed to >> brute-force searches to remove writable mappings. > > Fantastic (well, sort of)! > > If I understand it correctly, Todd is using PV drivers in Linux HVM guests, > so the reason for brute-force search is due to former L1 page-tables being > used as I/O pages, not being unshadowed because they can get writable > mappings out of it. > It is, shortly, an unshadowing problem. Should be `easy` to fix. I wasn't > using PV drivers, so I was not experiencing this behaviour. > > Or, it could be a fixup table bug, but I doubt it. > > George, did you saw excessive fixup faults in the trace? > > Todd, could you try without PV drivers (plain qemu emulation) and see if the > results get better? To the best of my knowledge, I am not using PV on HVM drivers since they are not upstream. I am using 2.6.27-rc4 xen domU kernel, with the normal xen PV drivers and KVM virtio built in. Am I mistaken? I am running the test with shadow3 disabled now. I'll report the results when they come out. Any other suggestions or things for me to try, let me know. Cheers, Todd _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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