[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] FW: VT-d async invalidation for Device-TLB.
> 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. 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? Quan > Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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