[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Is there data copy between dom0 and domU
On Wed, Apr 23, 2014 at 03:40:25PM -0400, xu cong wrote: > 2014-04-23 12:22 GMT-04:00 Roger Pau Monné <roger.pau@xxxxxxxxxx>: > > > On 23/04/14 18:14, Wei Liu wrote: > > > 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. > > > > For disks, up to Linux 3.8 data is never copied and starting from 3.8 > > data can be copied (in the frontend) if both DomU and Dom0 are running > > Linux kernel >= 3.8. > > > > Roger. > > > > > What's the vif irq for? The following is my understanding, I am sure it is > correct or not. > When a packet arrives at physical machine, dom0 picks it up from NIC and > puts it to ring buffer, then notify the destination domU. (Are all of them Yes. > done by vif kernel thread?) So the vif irq is issued when dom0 notifies the For the guest RX path, yes. > destination domU, because vif is the virtual device of domU. If it is > correct, the vif irq (xen-dyn-event) is an event (softirq?) on the event > channel between dom0 and domU. While, if the vif irq processing does not > happens on the same core where destination domU is running, one IPI is > issued to finish the notification. > Softirq in Linux refers to a specific type of bottom-half mechanism; IPI in general means inter-processor interrupt. IIRC xen-dyn-event refers to event channel event. You might want to distinguish several concepts before moving on. Wei. > Regards, > Cong _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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