On 2020/4/17 下午12:19, Jason Wang wrote:
On 2020/4/15 上午12:20, Michael S. Tsirkin wrote:
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.
Good point, so in this case, the doorbell of control vq must
exclusively own a page.
Or we need intercept the doorbells that share a page with control vq
doorbell.
Thanks
Or to facilitate the hardware design, we may introduce dedicated
notification area for control vq?
Thanks
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]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
