2014-10-15 14:30 GMT-04:00 David Xu <davidxu06@xxxxxxxxx>: > 2014-09-29 5:04 GMT-04:00 Michael S. Tsirkin <mst@xxxxxxxxxx>: >> On Wed, Sep 24, 2014 at 02:40:53PM -0400, David Xu wrote: >>> Hi Michael, >>> >>> I found this interesting project from KVM TODO website: >>> >>> allow handling short packets from softirq or VCPU context >>> Plan: >>> We are going through the scheduler 3 times >>> (could be up to 5 if softirqd is involved) >>> Consider RX: host irq -> io thread -> VCPU thread -> >>> guest irq -> guest thread. >>> This adds a lot of latency. >>> We can cut it by some 1.5x if we do a bit of work >>> either in the VCPU or softirq context. >>> Testing: netperf TCP RR - should be improved drastically >>> netperf TCP STREAM guest to host - no regression >>> >>> Would you mind saying more about the work either in the vCPU or >>> softirq context? >> >> For TX, we might be able to execute it directly from VCPU context. >> For RX, from softirq context. >> Do you mean for RX, we directly put data to a shared buffer accessed by guest VM bypassing the IO thread? For TX, in vCPU context network data is added to the shared buffer and kick host IRQ to send them? >>> Why it is only for short packets handling? >> >> That's just one idea to avoid doing too much work like this. >> >> Doing too much work in VCPU context would break pipelining, >> likely degrading stream performance. >> Work in softirq context is not accounted against the correct >> cgroups, doing a lot of work there will mean guest can steal >> CPU from other guests. >> >>> Thanks a >>> lot! >>> >>> >>> Regards, >>> >>> Cong -- 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
