virtio — archive

[OASIS Issue Tracker] Created: (VIRTIO-13) Remove VIRTIO_F_NOTIFY_ON_EMPTY?

From: Rusty Russell <[email protected]>
To: [email protected]
Date: Mon, 19 Aug 2013 08:32:00 -0000

OASIS Issues Tracker <[email protected]> writes: > Remove VIRTIO_F_NOTIFY_ON_EMPTY? > --------------------------------- > > Key: VIRTIO-13 > URL: http://tools.oasis-open.org/issues/browse/VIRTIO-13 > Project: OASIS Virtual I/O Device (VIRTIO) TC > Issue Type: Improvement > Reporter: Rusty Russell > > > Notify on empty means that the device interrupts even if it wouldn't normally, in the case where a normally-full virtqueue is empty. > > ISTR this was a performance hack; it's no longer used in Linux anyway, and performance issues may have been due to a race which sometimes lost interrupts :) Which would look something like this: commit 3a4ec12fdf041e2d55c24d4aacfbba829bc228f8 Author: Rusty Russell <[email protected]> Date: Mon Aug 19 18:00:35 2013 +0930 Remove VIRTIO_F_NOTIFY_ON_EMPTY As per http://tools.oasis-open.org/issues/browse/VIRTIO-13 Signed-off-by: Rusty Russell <[email protected]> diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt index 3e311ec..353ef44 100644 --- a/virtio-v1.0-wd01-part1-specification.txt +++ b/virtio-v1.0-wd01-part1-specification.txt @@ -1302,9 +1302,7 @@ the different features the driver negotiated. Often a driver will suppress transmission interrupts using the VRING_AVAIL_F_NO_INTERRUPT flag (see 2.4.2 Receiving Used Buffers From The Device) and check for used packets in the transmit path of following -packets. However, it will still receive interrupts if the -VIRTIO_F_NOTIFY_ON_EMPTY feature is negotiated, indicating that -the transmission queue is completely emptied. +packets. The normal behavior in this interrupt handler is to retrieve and new descriptors from the used ring and free the corresponding @@ -2498,18 +2496,7 @@ contents of the event field. The following events are defined: 2.6 Reserved Feature Bits ========================= -Currently there are four device-independent feature bits defined: - - VIRTIO_F_NOTIFY_ON_EMPTY (24) Negotiating this feature - indicates that the driver wants an interrupt if the device runs - out of available descriptors on a virtqueue, even though - interrupts are suppressed using the VRING_AVAIL_F_NO_INTERRUPT - flag or the used_event field. An example of this is the - networking driver: it doesn't need to know every time a packet - is transmitted, but it does need to free the transmitted - packets a finite time after they are transmitted. It can avoid - using a timer if the device interrupts it when all the packets - are transmitted. +Currently there are three device-independent feature bits defined: VIRTIO_F_ANY_LAYOUT (27) This feature indicates that the device accepts arbitrary descriptor layouts, as described in Section FIXME.