Re: [Xen-devel] [PATCH V4 2/3] xen-netback: switch to NAPI + kthread 1:1 model

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Aug 06, 2013 at 04:50:02PM +0100, Ian Campbell wrote:
> On Tue, 2013-08-06 at 16:47 +0100, Wei Liu wrote:
> > On Tue, Aug 06, 2013 at 04:38:56PM +0100, Ian Campbell wrote:
> > [...]
> > > >  * An example sequence of head fields (I = INVALID_PENDING_RING_IDX):
> > > >  *
> > > >  * ...|0 I I I|5 I|9 I I I|...
> > > >  * -->|<-INUSE----------------
> > > >  *
> > > >  * After consuming the first slot(s) we have:
> > > >  *
> > > >  * ...|V V V V|5 I|9 I I I|...
> > > >  * -----FREE->|<-INUSE--------
> > > >  *
> > > >  * where V stands for "valid pending ring index". Any number other
> > > >  * than INVALID_PENDING_RING_IDX is OK. In practice we use 0.
> > > 
> > > Perhaps add "These entries are considered free and can contain any
> > > number other than INVALID_PENDING_RING_IDX" ?
> > > 
> > > Do you have a #define, like FREE_PENDING_RING_IDX for this value? Should
> > > mention it if so I think.
> > > 
> > 
> > Unfortunately no. This can be fixed later with separate patch? Or just
> > have that change in this patch?
> 
> Separate I think, this patch is already pretty unwieldy.
> 

So the comment for now:

/* For the head field in pending_tx_info: it is used to indicate
 * whether this tx info is the head of one or more coalesced requests.
 *
 * When head != INVALID_PENDING_RING_IDX, it means the start of a new
 * tx requests queue and the end of previous queue.
 *
 * An example sequence of head fields (I = INVALID_PENDING_RING_IDX):
 *
 * ...|0 I I I|5 I|9 I I I|...
 * -->|<-INUSE----------------
 *
 * After consuming the first slot(s) we have:
 *
 * ...|V V V V|5 I|9 I I I|...
 * -----FREE->|<-INUSE--------
 *
 * where V stands for "valid pending ring index". Any number other
 * than INVALID_PENDING_RING_IDX is OK. These entries are considered
 * free and can contain any number other than
 * INVALID_PENDING_RING_IDX. In practice we use 0.
 *
 * The in use non-INVALID_PENDING_RING_IDX (say 0, 5 and 9 in the
 * above example) number is the index into pending_tx_info and
 * mmap_pages arrays.
 */


The FREE_PENDING_RING_IDX will be added with later patch.


Wei.

> > 
> > 
> > Wei.
> > 
> > > >  *
> > > >  * The non-INVALID_PENDING_RING_IDX (say 0, 5 and 9 in the above
> > >         ^ add "in use"?
> > > 
> > > >  * example) number is the index into pending_tx_info and mmap_pages
> > > >  * arrays.
> > > >  */
> > > > 
> > > > > 
> > > > > Wei.
> > > > > 
> > > > > > Ian.
> > > 
> 

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