netdev - Re: [PATCH] xen/netfront: handle compound page fragments on transmit

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Message-ID: <1946803246.20121120144522@eikelenboom.it>
Date:	Tue, 20 Nov 2012 14:45:22 +0100
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Stefan Bader <stefan.bader@...onical.com>
CC:	Ian Campbell <ian.campbell@...rix.com>, netdev@...r.kernel.org,
	<xen-devel@...ts.xen.org>, Eric Dumazet <edumazet@...gle.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	ANNIE LI <annie.li@...cle.com>
Subject: Re: [PATCH] xen/netfront: handle compound page fragments on transmit


Tuesday, November 20, 2012, 2:30:54 PM, you wrote:

> Aside from Jans comments about error handling, I tried below patch and it seems
> to solve the problem with transfers out of the domU for me (though only shallow
> testing done, otoh 5 times is more than getting stuck the first time).

> -Stefan

I'm running with this patch now, it seems to fix the problems for me as well.

--
Sander

> On 20.11.2012 12:40, Ian Campbell wrote:
>> An SKB paged fragment can consist of a compound page with order > 0.
>> However the netchannel protocol deals only in PAGE_SIZE frames.
>> 
>> Handle this in xennet_make_frags by iterating over the frames which
>> make up the page.
>> 
>> This is the netfront equivalent to 6a8ed462f16b for netback.
>> 
>> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
>> Cc: netdev@...r.kernel.org
>> Cc: xen-devel@...ts.xen.org
>> Cc: Eric Dumazet <edumazet@...gle.com>
>> Cc: Konrad Rzeszutek Wilk <konrad@...nel.org>
>> Cc: ANNIE LI <annie.li@...cle.com>
>> Cc: Sander Eikelenboom <linux@...elenboom.it>
>> Cc: Stefan Bader <stefan.bader@...onical.com>
> Tested-by: Stefan Bader <stefan.bader@...onical.com>
>> ---
>>  drivers/net/xen-netfront.c |   58 +++++++++++++++++++++++++++++++++----------
>>  1 files changed, 44 insertions(+), 14 deletions(-)
>> 
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index caa0110..a12b99a 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -452,24 +452,54 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
>>       /* Grant backend access to each skb fragment page. */
>>       for (i = 0; i < frags; i++) {
>>               skb_frag_t *frag = skb_shinfo(skb)->frags + i;
>> +             struct page *page = skb_frag_page(frag);
>> +             unsigned long size = skb_frag_size(frag);
>> +             unsigned long offset = frag->page_offset;
>>  
>> -             tx->flags |= XEN_NETTXF_more_data;
>> +             /* Data must not cross a page boundary. */
>> +             BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
>>  
>> -             id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
>> -             np->tx_skbs[id].skb = skb_get(skb);
>> -             tx = RING_GET_REQUEST(&np->tx, prod++);
>> -             tx->id = id;
>> -             ref = gnttab_claim_grant_reference(&np->gref_tx_head);
>> -             BUG_ON((signed short)ref < 0);
>> +             /* Skip unused frames from start of page */
>> +             page += offset >> PAGE_SHIFT;
>> +             offset &= ~PAGE_MASK;
>>  
>> -             mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
>> -             gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
>> -                                             mfn, GNTMAP_readonly);
>> +             while (size > 0) {
>> +                     unsigned long bytes;
>>  
>> -             tx->gref = np->grant_tx_ref[id] = ref;
>> -             tx->offset = frag->page_offset;
>> -             tx->size = skb_frag_size(frag);
>> -             tx->flags = 0;
>> +                     BUG_ON(offset >= PAGE_SIZE);
>> +
>> +                     bytes = PAGE_SIZE - offset;
>> +                     if (bytes > size)
>> +                             bytes = size;
>> +
>> +                     tx->flags |= XEN_NETTXF_more_data;
>> +
>> +                     id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
>> +                     np->tx_skbs[id].skb = skb_get(skb);
>> +                     tx = RING_GET_REQUEST(&np->tx, prod++);
>> +                     tx->id = id;
>> +                     ref = gnttab_claim_grant_reference(&np->gref_tx_head);
>> +                     BUG_ON((signed short)ref < 0);
>> +
>> +                     mfn = pfn_to_mfn(page_to_pfn(page));
>> +                     gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
>> +                                                     mfn, GNTMAP_readonly);
>> +
>> +                     tx->gref = np->grant_tx_ref[id] = ref;
>> +                     tx->offset = offset;
>> +                     tx->size = bytes;
>> +                     tx->flags = 0;
>> +
>> +                     offset += bytes;
>> +                     size -= bytes;
>> +
>> +                     /* Next frame */
>> +                     if (offset == PAGE_SIZE && size) {
>> +                             BUG_ON(!PageCompound(page));
>> +                             page++;
>> +                             offset = 0;
>> +                     }
>> +             }
>>       }
>>  
>>       np->tx.req_prod_pvt = prod;
>> 



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