[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH 0/2] ASID: Flush by ASID
It begs the question whether it's worth complicating code for an optimisation with no measurable benefit, doesn't it? -- Keir On 12/01/2011 12:41, "Wei Wang2" <wei.wang2@xxxxxxx> wrote: > Hi Tim, > Flush by ASID provides more flexible control of tlb flushing. The most > advantage is to allow hypervisor to flush tagged tlb selectively. Using this > feature, HV is able to flush tlb entries associated with a guest VM directly > instead of allocating a new asid . The whole tlb flush will also be reduced > by reducing asid allocation. > > So far, we did not measure drastic performance improvement in testing with > kernbench and X11perf. Actually, we found out that, reducing tlb flushes > accompanying with vmrun does not improve performance very much. > we sent out a patch to optimize hvm_flush_guest_tlbs last week, which reduces > over 90% tlb flushes for vmrun, and we even cannot see signification speedup > with it. Maybe, the latency of vmrun is too big so that the overhead of tlb > flush is negligible? > > Thanks, > Wei > > > On Wednesday 12 January 2011 11:17:00 Tim Deegan wrote: >> At 17:55 +0000 on 11 Jan (1294768552), Wei Wang2 wrote: >>> Future AMD SVM supports a new feature called flush by ASID. The idea is >>> to allow CPU to flush TLBs associated with the ASID assigned to guest VM. >>> So hypervisor doesn't have to reassign a new ASID in order to flush >>> guest's VCPU. Please review it. >> >> What advantage does the new system have? Intuitively it seems like it >> might be a tiny bit fairer and a tiny bit faster (by explicitly flushing >> instead of relying on LRO) but I'm not convinced that it will be visible >> in macro-benchmarks. Have you measured it? >> >> Cheers, >> >> Tim. >> >>> Thanks, >>> Wei >>> >>> Signed-off-by: Wei Huang <wei.huang2@xxxxxxx> >>> Signed-off-by: Wei Wang <wei.wang2@xxxxxxx> >>> -- >>> Advanced Micro Devices GmbH >>> Sitz: Dornach, Gemeinde Aschheim, >>> Landkreis München Registergericht München, >>> HRB Nr. 43632 >>> WEEE-Reg-Nr: DE 12919551 >>> Geschäftsführer: >>> Alberto Bozzo, Andrew Bowd >>> >>> >>> _______________________________________________ >>> Xen-devel mailing list >>> Xen-devel@xxxxxxxxxxxxxxxxxxx >>> http://lists.xensource.com/xen-devel > > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
![]() |
Lists.xenproject.org is hosted with RackSpace, monitoring our |