From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v2 1/1] xen/netback: correctly calculate required slots of skb. Date: Thu, 11 Jul 2013 10:47:58 +0100 Message-ID: <1373536078.5453.159.camel@hastur.hellion.org.uk> References: <1373447711-31303-1-git-send-email-annie.li@oracle.com> <1373530274.5453.148.camel@hastur.hellion.org.uk> <51DE6DFD.9080007@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , , , , To: annie li Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:12912 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754276Ab3GKJsD (ORCPT ); Thu, 11 Jul 2013 05:48:03 -0400 In-Reply-To: <51DE6DFD.9080007@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2013-07-11 at 16:34 +0800, annie li wrote: > On 2013-7-11 16:11, Ian Campbell wrote: > > On Wed, 2013-07-10 at 17:15 +0800, Annie Li wrote: > >> +static int netbk_count_slots(struct xenvif *vif, struct sk_buff *skb, > >> + int *copy_off, unsigned long size, > >> + unsigned long offset, int *head) > >> { > >> - unsigned int count; > >> - int i, copy_off; > >> + unsigned long bytes; > >> + int count = 0; > >> > >> - count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE); > >> + offset &= ~PAGE_MASK; > >> > >> - copy_off = skb_headlen(skb) % PAGE_SIZE; > >> + while (size > 0) { > >> + BUG_ON(offset >= PAGE_SIZE); > >> + BUG_ON(*copy_off > MAX_BUFFER_OFFSET); > >> > >> - if (skb_shinfo(skb)->gso_size) > >> - count++; > >> + bytes = PAGE_SIZE - offset; > >> > >> - for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { > >> - unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]); > >> - unsigned long offset = skb_shinfo(skb)->frags[i].page_offset; > >> - unsigned long bytes; > >> + if (bytes > size) > >> + bytes = size; > >> > >> - offset &= ~PAGE_MASK; > >> + if (start_new_rx_buffer(*copy_off, bytes, *head)) { > >> + count++; > >> + *copy_off = 0; > >> + } > >> > >> - while (size > 0) { > >> - BUG_ON(offset >= PAGE_SIZE); > >> - BUG_ON(copy_off > MAX_BUFFER_OFFSET); > >> + if (*copy_off + bytes > MAX_BUFFER_OFFSET) > >> + bytes = MAX_BUFFER_OFFSET - *copy_off; > >> > >> - bytes = PAGE_SIZE - offset; > >> + *copy_off += bytes; > >> > >> - if (bytes > size) > >> - bytes = size; > >> + offset += bytes; > >> + size -= bytes; > >> > >> - if (start_new_rx_buffer(copy_off, bytes, 0)) { > >> - count++; > >> - copy_off = 0; > >> - } > >> + /* Next frame */ > >> + if (offset == PAGE_SIZE && size) > >> + offset = 0; > >> + > >> + if (*head) > >> + count++; > > This little bit corresponds to the "/* Leave a gap for the GSO > > descriptor. */" in gop_frag_copy? > > No, it does not correspond to this in gop_frag_copy. So what does it correspond to? > The code here only > increase count for the first time. I thought to initialize the count in > xen_netbk_count_skb_slots with 1 to avoid this. But thinking of the > extreme case when the header size is zero(not sure whether this case > could be true), I increase the count here to keep safe in case header > size is zero. netfront requires that the first slot always contains some data, gop_frag_copy will BUG if that's not the case. > > There is code correspond to that in gop_frag_copy in > xen_netbk_count_skb_slots, see following, > > + if (skb_shinfo(skb)->gso_size && !vif->gso_prefix) > + count++; > (The original code does not have gso_prefix, I added it in this patch > too based on Wei's suggestion) OK. It's be nice if the count and copy variants of this logic could be as similar as possible but they already differ quite a bit. I have considered whether we could combine the two by adding "dry-run" functionality to gop_frag_copy but that seems like it would just ugly up both versions. Ian. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v2 1/1] xen/netback: correctly calculate required slots of skb. Date: Thu, 11 Jul 2013 10:47:58 +0100 Message-ID: <1373536078.5453.159.camel@hastur.hellion.org.uk> References: <1373447711-31303-1-git-send-email-annie.li@oracle.com> <1373530274.5453.148.camel@hastur.hellion.org.uk> <51DE6DFD.9080007@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51DE6DFD.9080007@oracle.com> Sender: netdev-owner@vger.kernel.org To: annie li Cc: xen-devel@lists.xensource.com, netdev@vger.kernel.org, wei.liu2@citrix.com, konrad.wilk@oracle.com, msw@amazon.com List-Id: xen-devel@lists.xenproject.org On Thu, 2013-07-11 at 16:34 +0800, annie li wrote: > On 2013-7-11 16:11, Ian Campbell wrote: > > On Wed, 2013-07-10 at 17:15 +0800, Annie Li wrote: > >> +static int netbk_count_slots(struct xenvif *vif, struct sk_buff *skb, > >> + int *copy_off, unsigned long size, > >> + unsigned long offset, int *head) > >> { > >> - unsigned int count; > >> - int i, copy_off; > >> + unsigned long bytes; > >> + int count = 0; > >> > >> - count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE); > >> + offset &= ~PAGE_MASK; > >> > >> - copy_off = skb_headlen(skb) % PAGE_SIZE; > >> + while (size > 0) { > >> + BUG_ON(offset >= PAGE_SIZE); > >> + BUG_ON(*copy_off > MAX_BUFFER_OFFSET); > >> > >> - if (skb_shinfo(skb)->gso_size) > >> - count++; > >> + bytes = PAGE_SIZE - offset; > >> > >> - for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { > >> - unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]); > >> - unsigned long offset = skb_shinfo(skb)->frags[i].page_offset; > >> - unsigned long bytes; > >> + if (bytes > size) > >> + bytes = size; > >> > >> - offset &= ~PAGE_MASK; > >> + if (start_new_rx_buffer(*copy_off, bytes, *head)) { > >> + count++; > >> + *copy_off = 0; > >> + } > >> > >> - while (size > 0) { > >> - BUG_ON(offset >= PAGE_SIZE); > >> - BUG_ON(copy_off > MAX_BUFFER_OFFSET); > >> + if (*copy_off + bytes > MAX_BUFFER_OFFSET) > >> + bytes = MAX_BUFFER_OFFSET - *copy_off; > >> > >> - bytes = PAGE_SIZE - offset; > >> + *copy_off += bytes; > >> > >> - if (bytes > size) > >> - bytes = size; > >> + offset += bytes; > >> + size -= bytes; > >> > >> - if (start_new_rx_buffer(copy_off, bytes, 0)) { > >> - count++; > >> - copy_off = 0; > >> - } > >> + /* Next frame */ > >> + if (offset == PAGE_SIZE && size) > >> + offset = 0; > >> + > >> + if (*head) > >> + count++; > > This little bit corresponds to the "/* Leave a gap for the GSO > > descriptor. */" in gop_frag_copy? > > No, it does not correspond to this in gop_frag_copy. So what does it correspond to? > The code here only > increase count for the first time. I thought to initialize the count in > xen_netbk_count_skb_slots with 1 to avoid this. But thinking of the > extreme case when the header size is zero(not sure whether this case > could be true), I increase the count here to keep safe in case header > size is zero. netfront requires that the first slot always contains some data, gop_frag_copy will BUG if that's not the case. > > There is code correspond to that in gop_frag_copy in > xen_netbk_count_skb_slots, see following, > > + if (skb_shinfo(skb)->gso_size && !vif->gso_prefix) > + count++; > (The original code does not have gso_prefix, I added it in this patch > too based on Wei's suggestion) OK. It's be nice if the count and copy variants of this logic could be as similar as possible but they already differ quite a bit. I have considered whether we could combine the two by adding "dry-run" functionality to gop_frag_copy but that seems like it would just ugly up both versions. Ian.