Re: [Xen-devel] Is there data copy between dom0 and domU

[xu cong <congxumail@xxxxxxxxx>]

2014-04-23 12:14 GMT-04:00 Wei Liu <wei.liu2@xxxxxxxxxx>:

On Wed, Apr 23, 2014 at 12:06:51PM -0400, xu cong wrote:
> When applications running in domU receive/send data from/to network, is
> there data copy via shared memory between dom0 and domU? Or the zero copy
> is used. How about the disk I/O operations? Thanks.

If you're using latest kernel (3.14-ish), guest TX path is zero-copy,
otherwise it's using copy. For RX path it always copies.

I think disk always copies data. But I'm not sure.

Wei.

I am using the 3.12. So the cpu utilization (top output) of vifx.0 process in dom0 is for data copy and irq processing, right? I found that if the vif irq processing is on the same core where the corresponding domU is running, the CPU utilization of dom0 is lower and the application IOPS is higher. I think maybe it is caused by less IPIs are issued.

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