On 05/24/2010 11:05 AM, Michael S. Tsirkin wrote:
>
> Okay, but why is lockunshare faster than unshare?
>
>
No idea.
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On Mon, May 24, 2010 at 09:37:05AM +0300, Avi Kivity wrote:
> On 05/23/2010 07:30 PM, Michael S. Tsirkin wrote:
>>
>>
Maybe we should use atomics on index then?
>>> This should only be helpful if you access the cacheline several times in
>>> a row. That's not the case in
On 05/23/2010 07:30 PM, Michael S. Tsirkin wrote:
>
>
>>> Maybe we should use atomics on index then?
>>>
>>>
>> This should only be helpful if you access the cacheline several times in
>> a row. That's not the case in virtio (or here).
>>
> So why does it help?
>
We actually
On Sun, May 23, 2010 at 07:03:10PM +0300, Avi Kivity wrote:
> On 05/23/2010 06:51 PM, Michael S. Tsirkin wrote:
>>>
So locked version seems to be faster than unlocked,
and share/unshare not to matter?
>>> May be due to the processor using the LOCK operation as a hint to
On Sun, May 23, 2010 at 07:03:10PM +0300, Avi Kivity wrote:
> On 05/23/2010 06:51 PM, Michael S. Tsirkin wrote:
>>>
So locked version seems to be faster than unlocked,
and share/unshare not to matter?
>>> May be due to the processor using the LOCK operation as a hint to
On 05/23/2010 06:51 PM, Michael S. Tsirkin wrote:
>>
>>> So locked version seems to be faster than unlocked,
>>> and share/unshare not to matter?
>>>
>>>
>> May be due to the processor using the LOCK operation as a hint to
>> reserve the cacheline for a bit.
>>
> Maybe we should use a
On Thu, May 20, 2010 at 02:38:16PM +0930, Rusty Russell wrote:
> On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
> > On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
> > > > Note that this is a exclusive->shared->exclusive bounce only, too.
> > > >
> > >
> > > A bounce is a bounce.
> >
On Sun, May 23, 2010 at 06:41:33PM +0300, Avi Kivity wrote:
> On 05/23/2010 06:31 PM, Michael S. Tsirkin wrote:
>> On Thu, May 20, 2010 at 02:38:16PM +0930, Rusty Russell wrote:
>>
>>> On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
>>>
On Wed, 19 May 2010 05:36:42 pm Avi Kivity
On 05/23/2010 06:31 PM, Michael S. Tsirkin wrote:
> On Thu, May 20, 2010 at 02:38:16PM +0930, Rusty Russell wrote:
>
>> On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
>>
>>> On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
>>>
> Note that this is a exclusive->shared->ex
On Thu, May 20, 2010 at 02:38:16PM +0930, Rusty Russell wrote:
> On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
> > On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
> > > > Note that this is a exclusive->shared->exclusive bounce only, too.
> > > >
> > >
> > > A bounce is a bounce.
> >
On 05/20/2010 05:34 PM, Rusty Russell wrote:
>
>> Have just one ring, no indexes. The producer places descriptors into
>> the ring and updates the head, The consumer copies out descriptors to
>> be processed and copies back in completed descriptors. Chaining is
>> always linear. The descriptors
On Thu, 20 May 2010 04:30:56 pm Avi Kivity wrote:
> On 05/20/2010 08:01 AM, Rusty Russell wrote:
> >
> >> A device with out of order
> >> completion (like virtio-blk) will quickly randomize the unused
> >> descriptor indexes, so every descriptor fetch will require a bounce.
> >>
> >> In contrast, i
On Thu, May 20, 2010 at 02:31:50PM +0930, Rusty Russell wrote:
> Can we do better? The obvious idea is to try to get rid of last_used and
> used, and use the ring itself. We would use an invalid entry to mark the
> head of the ring.
>
> Any other thoughts?
> Rusty.
We also need a way to avoid i
On 05/20/2010 08:01 AM, Rusty Russell wrote:
>
>> A device with out of order
>> completion (like virtio-blk) will quickly randomize the unused
>> descriptor indexes, so every descriptor fetch will require a bounce.
>>
>> In contrast, if the rings hold the descriptors themselves instead of
>> pointe
On 05/20/2010 01:33 AM, Michael S. Tsirkin wrote:
>
>> Virtio is already way too bouncy due to the indirection between the
>> avail/used rings and the descriptor pool. A device with out of order
>> completion (like virtio-blk) will quickly randomize the unused
>> descriptor indexes, so every descr
On Thu, 20 May 2010 02:31:50 pm Rusty Russell wrote:
> On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
> > > Note that this is a exclusive->shared->exclusive bounce only, too.
> > >
> >
> > A bounce is a bounce.
>
> I tried to measure this to show that you were wrong, but I was only able
>
On Wed, 19 May 2010 05:36:42 pm Avi Kivity wrote:
> > Note that this is a exclusive->shared->exclusive bounce only, too.
> >
>
> A bounce is a bounce.
I tried to measure this to show that you were wrong, but I was only able
to show that you're right. How annoying. Test code below.
> Virtio
On Wed, May 19, 2010 at 11:06:42AM +0300, Avi Kivity wrote:
> On 05/19/2010 10:39 AM, Rusty Russell wrote:
>>
>> I think we're talking about the last 2 entries of the avail ring. That means
>> the worst case is 1 false bounce every time around the ring.
>
> It's low, but why introduce an inefficie
On 05/19/2010 10:39 AM, Rusty Russell wrote:
>
> I think we're talking about the last 2 entries of the avail ring. That means
> the worst case is 1 false bounce every time around the ring.
It's low, but why introduce an inefficiency when you can avoid doing it
for the same effort?
> I think tha
On Wed, 12 May 2010 04:57:22 am Avi Kivity wrote:
> On 05/07/2010 06:23 AM, Rusty Russell wrote:
> > On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote:
> >
> >> On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
> >>
> >>> + /* We publish the last-seen used index at the end of the available
On Tue, May 11, 2010 at 10:27:22PM +0300, Avi Kivity wrote:
> On 05/07/2010 06:23 AM, Rusty Russell wrote:
>> On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote:
>>
>>> On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
>>>
+ /* We publish the last-seen used index at the end of the avai
On 05/07/2010 06:23 AM, Rusty Russell wrote:
> On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote:
>
>> On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
>>
>>> + /* We publish the last-seen used index at the end of the available ring.
>>> +* It is at the end for backwards compatibilit
On Thu, 6 May 2010 07:30:00 pm Avi Kivity wrote:
> On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
> > + /* We publish the last-seen used index at the end of the available ring.
> > +* It is at the end for backwards compatibility. */
> > + vr->last_used_idx =&(vr)->avail->ring[num];
> > +
On 05/05/2010 11:58 PM, Michael S. Tsirkin wrote:
> + /* We publish the last-seen used index at the end of the available ring.
> + * It is at the end for backwards compatibility. */
> + vr->last_used_idx =&(vr)->avail->ring[num];
> + /* Verify that last used index does not spill ov
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