[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] FW: VT-d async invalidation for Device-TLB.
>>> On 18.06.15 at 10:09, <quan.xu@xxxxxxxxx> wrote: >> On 16.06.15 09:59, <mailto:JBeulich@xxxxxxxx> wrote: >> >>> On 16.06.15 at 09:59, <yang.z.zhang@xxxxxxxxx> wrote: >> > Jan Beulich wrote on 2015-06-16: >> >>>>> On 16.06.15 at 05:07, <yang.z.zhang@xxxxxxxxx> wrote: >> >>> Jan Beulich wrote on 2015-06-15: >> >>>>>>> On 13.06.15 at 16:44, <quan.xu@xxxxxxxxx> wrote: >> >>>>>> On 12.06.15 at 14:47, <JBeulich@xxxxxxxx> wrote: >> >>>>>>>>> On 12.06.15 at 04:40, <quan.xu@xxxxxxxxx> wrote: > >> > >> > which one? 1.4us for sync case and 4.3us for async case? >> >> The difference between the two (i.e. why is the async variant three times as >> long). >> > > I have tested iotlb async/sync invalidation to get another data. Also I > disabled 'P State' / 'C State' in bios. > For async invalidation: about 2.67 us. > For sync invalidation: about 1.28 us. > > I also tested VCPU_KICK_SOFTIRQ irq cost. > When hypervisor calls cpu_raise_softirq(..VCPU_KICK_SOFTIRQ) to raise an > VCPU_KICK_SOFTIRQ irq, and vcpu_kick_softirq() is the VCPU_KICK_SOFTIRQ > interrupt handler. > I got the cost between cpu_raise_softirq(..VCPU_KICK_SOFTIRQ) and > vcpu_kick_softirq(). It is about 1.21 us. > > I think the difference is interrupt cost between async invalidation and sync > invalidation. Which contradicts what I think Yang said in an earlier reply. > 2.67us is almost ideal for async invalidation cost. There are 4 reasons to > cost much more time: > 1. If enable 'P State' / 'C State' in bios. > 2. Hypervisor is running in No-root mode. > 3. The time doesn't include the cost of handling of interrupt. I just > record it at the entry of interrupt handler. > 4. More pass-through VMs runs. > > So there are maybe some performance issues when we replace the current > spinning for the non-ATS case. > We can start from ATS case firstly, And apply it to non-ATS case later if the > async approach performance is acceptable. > Jan, Do you agree with this? No, I'm still not convinced that leaving the non-ATS case alone initially is the right approach. But maybe I'm the only one? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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