Hi Jan, On 2012/09/07 17:26, Jan Kiszka wrote: > On 2012-09-06 13:27, Tomoki Sekiyama wrote: >> This RFC patch series provides facility to dedicate CPUs to KVM guests >> and enable the guests to handle interrupts from passed-through PCI devices >> directly (without VM exit and relay by the host). >> >> With this feature, we can improve throughput and response time of the device >> and the host's CPU usage by reducing the overhead of interrupt handling. >> This is good for the application using very high throughput/frequent >> interrupt device (e.g. 10GbE NIC). >> Real-time applicatoins also gets benefit from CPU isolation feature, which >> reduces interfare from host kernel tasks and scheduling delay. >> >> The overview of this patch series is presented in CloudOpen 2012. >> The slides are available at: >> http://events.linuxfoundation.org/images/stories/pdf/lcna_co2012_sekiyama.pdf > > One question regarding your benchmarks: If you measured against standard > KVM, were the vCPU thread running on an isolcpus core of its own as > well? If not, your numbers about the impact of these patches on maximum, > maybe also average latencies are likely too good. Also, using a non-RT > host and possibly a non-prioritized vCPU thread for the standard > scenario looks like an unfair comparison. In the standard KVM benchmark, the vCPU thread is pinned down to its own CPU core. In addition, the vCPU thread and irq/*-kvm threads are both set to the max priority with SCHED_RR policy. As you said, RT-host may result in better max latencies as below. (But min/average latencies became worse, however, this might be our setup issue.) Min / Avg / Max latencies Normal KVM RT-host (3.4.4-rt14) 15us / 21us / 117us non RT-host (3.5.0-rc6) 6us / 11us / 152us KVM + Direct IRQ non RT-host (3.5.0-rc6 +patch) 1us / 2us / 14us Thanks, -- Tomoki Sekiyama <tomoki.sekiyama.qu@xxxxxxxxxxx> Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
