On Tue, Apr 14, 2020 at 01:12:51PM +0000, Vitaly Mireyno wrote: > > >-----Original Message----- > >From: [email protected] > ><[email protected]> On Behalf > >Of Jason Wang > >Sent: Tuesday, 7 April, 2020 10:56 > >To: [email protected]; Virtio-Dev > ><[email protected]> > >Cc: Michael S. Tsirkin <[email protected]> > >Subject: [Virtio-networking] Doorbell mapping of vDPA > > > >---------------------------------------------------------------------- > >Hi all: > > > >To get native performance of VF, we need to map doorbell to guest to avoid > >unnecessary vmexit. In > >order to do this, we will launch qemu with page-per-vq=on. This means the > >each doorbell register > >should be located at the beginning of 4K page and does not share the page > >with other registers. Then > >vDPA framework can safely map it into the guest physical address (GPA) range > >defined by qemu. It > >could be either > > > >1) a single doorbell register that is used by all virtqueues > > > >or > > > >2) several different per-vq doorbell registers > > > >If you decide to implement a virtio-pci register layout, need to make sure > >for notification structure > >(4.1.4.4 of virtio spec): > > > >For each virtqueue, the result > >ofcap.offset+queue_notify_off*notify_off_multiplier is PAGE_SIZE (e.g > >4K) alignment, and the doorbeel does not share the page with other registers. > > > >And it would be better if queue_notify_off, notify_off_multiplier can be > >changed via firmware for > >extra flexibility. > > > > In some cases, these conditions could not be met for a virtio-net hardware > device over PCI transport. > queue_notify and notify_off_multiplier could not always be fully controlled > by the firmware. There could be hardware limitations on flexibility degree of > these parameters. > Specifically, the limitations I'm thinking of are: > * queue_notify_off>0 and notify_off_multiplier>0 > * Several doorbell registers of several virtqueues share the same page (but > don't share the page with other registers). > > Can this be supported in vDPA with direct doorbell mapping? > > Thanks
There's value in being able to intercept some vqs in software while the rest of vqs are handled in hardware. E.g. that's the case for e.g. the control vq. > >Please check and make sure your hardware have such ability and feel free to > >ask if you have questions > >(offline if necessary). > > > >Thanks > > > > > > > > > > > >_______________________________________________ > >Virtio-networking mailing list > >[email protected] > >https://urldefense.proofpoint.com/v2/url?u=https-3A__www.redhat.com_mailman_listinfo_virtio- > >2Dnetworking&d=DwIGaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw > >4A_NO7xgI&m=pddgVCz- > >orGTuUXATJ4Dmi7vAXatG9w47AmULNC3V9A&s=5mfYWbLCjcZO8FcwDqgAc5bjE-H- > >4p5TBkRZqP3uMsQ&e= --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
