| Message ID | 87r4i1gadv.fsf@rustcorp.com.au (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 04/23/13 06:05, Rusty Russell wrote: > Laszlo Ersek <lersek@redhat.com> writes: >> Hi, >> >> (I'm not subscribed to either list,) >> >> using the word "descriptor" is misleading in the following sections: > > Yes, I like the use of 'descriptor chains'. This is a definite > improvement. > > Here's the diff I ended up with (massaged to minimize it). > > Thanks! > Rusty. > > --- virtio-spec.txt-old 2013-04-23 13:22:21.339158214 +0930 > +++ virtio-spec.txt 2013-04-23 13:34:14.055176464 +0930 > @@ -482,10 +482,10 @@ > > 2.3.4 Available Ring > > -The available ring refers to what descriptors we are offering the > -device: it refers to the head of a descriptor chain. The “flags” > +The available ring refers to what descriptor chains we are offering the > +device: each entry refers to the head of a descriptor chain. The “flags” > field is currently 0 or 1: 1 indicating that we do not need an > -interrupt when the device consumes a descriptor from the > +interrupt when the device consumes a descriptor chain from the > available ring. Alternatively, the guest can ask the device to > delay interrupts until an entry with an index specified by the “ > used_event” field is written in the used ring (equivalently, > @@ -671,16 +671,16 @@ > > avail->ring[avail->idx % qsz] = head; > > -However, in general we can add many descriptors before we update > -the “idx” field (at which point they become visible to the > -device), so we keep a counter of how many we've added: > +However, in general we can add many separate descriptor chains before we update > +the “idx” field (at which point they become visible to the device), > +so we keep a counter of how many we've added: > > avail->ring[(avail->idx + added++) % qsz] = head; > > 2.4.1.3 Updating The Index Field > > Once the idx field of the virtqueue is updated, the device will > -be able to access the descriptor entries we've created and the > +be able to access the descriptor chains we've created and the > memory they refer to. This is why a memory barrier is generally > used before the idx update, to ensure it sees the most up-to-date > copy. > Not sure if it's customary here or if you need it / want it, but anyway Reviewed-by: Laszlo Ersek <lersek@redhat.com> (Also I've fixed the OVMF driver; just reposting the patch today with a better commit message.) Thanks much! Laszlo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Laszlo Ersek <lersek@redhat.com> writes: > On 04/23/13 06:05, Rusty Russell wrote: >> Laszlo Ersek <lersek@redhat.com> writes: >>> Hi, >>> >>> (I'm not subscribed to either list,) >>> >>> using the word "descriptor" is misleading in the following sections: >> >> Yes, I like the use of 'descriptor chains'. This is a definite >> improvement. ... > Not sure if it's customary here or if you need it / want it, but anyway > > Reviewed-by: Laszlo Ersek <lersek@redhat.com> Not needed, but always useful to ahve confirmation that I didn't introduce another mistake while fixing my old ones! > (Also I've fixed the OVMF driver; just reposting the patch today with a > better commit message.) > > Thanks much! > Laszlo Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- virtio-spec.txt-old 2013-04-23 13:22:21.339158214 +0930 +++ virtio-spec.txt 2013-04-23 13:34:14.055176464 +0930 @@ -482,10 +482,10 @@ 2.3.4 Available Ring -The available ring refers to what descriptors we are offering the -device: it refers to the head of a descriptor chain. The “flags” +The available ring refers to what descriptor chains we are offering the +device: each entry refers to the head of a descriptor chain. The “flags” field is currently 0 or 1: 1 indicating that we do not need an -interrupt when the device consumes a descriptor from the +interrupt when the device consumes a descriptor chain from the available ring. Alternatively, the guest can ask the device to delay interrupts until an entry with an index specified by the “ used_event” field is written in the used ring (equivalently, @@ -671,16 +671,16 @@ avail->ring[avail->idx % qsz] = head; -However, in general we can add many descriptors before we update -the “idx” field (at which point they become visible to the -device), so we keep a counter of how many we've added: +However, in general we can add many separate descriptor chains before we update +the “idx” field (at which point they become visible to the device), +so we keep a counter of how many we've added: avail->ring[(avail->idx + added++) % qsz] = head; 2.4.1.3 Updating The Index Field Once the idx field of the virtqueue is updated, the device will -be able to access the descriptor entries we've created and the +be able to access the descriptor chains we've created and the memory they refer to. This is why a memory barrier is generally used before the idx update, to ensure it sees the most up-to-date copy.