Re: [Xen-devel] [PATCH net-next v1] xen-netback: make copy batch size configurable

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 13 November 2017 10:50
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; 'Joao
> Martins' <joao.m.martins@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH net-next v1] xen-netback: make copy batch
> size configurable
> 
> >>> On 13.11.17 at 11:33, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Joao Martins [mailto:joao.m.martins@xxxxxxxxxx]
> >> Sent: 10 November 2017 19:35
> >> --- a/drivers/net/xen-netback/netback.c
> >> +++ b/drivers/net/xen-netback/netback.c
> >> @@ -96,6 +96,11 @@ unsigned int xenvif_hash_cache_size =
> >> XENVIF_HASH_CACHE_SIZE_DEFAULT;
> >>  module_param_named(hash_cache_size, xenvif_hash_cache_size, uint,
> >> 0644);
> 
> Isn't the "owner-write" permission here ...
> 
> >> --- a/drivers/net/xen-netback/rx.c
> >> +++ b/drivers/net/xen-netback/rx.c
> >> @@ -168,11 +168,14 @@ static void xenvif_rx_copy_add(struct
> >> xenvif_queue *queue,
> >>                           struct xen_netif_rx_request *req,
> >>                           unsigned int offset, void *data, size_t len)
> >>  {
> >> +  unsigned int batch_size;
> >>    struct gnttab_copy *op;
> >>    struct page *page;
> >>    struct xen_page_foreign *foreign;
> >>
> >> -  if (queue->rx_copy.num == COPY_BATCH_SIZE)
> >> +  batch_size = min(xenvif_copy_batch_size, queue->rx_copy.size);
> >
> > Surely queue->rx_copy.size and xenvif_copy_batch_size are always
> identical?
> > Why do you need this statement (and hence stack variable)?
> 
> ... the answer to your question?

Yes, I guess it could be... but since there's no re-alloc code for the arrays I 
wonder whether the intention was to make this dynamic or not.

  Paul

> 
> Jan


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