From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH net-next 3/6] virtio-net: small optimization on free_old_xmit_skbs() Date: Wed, 15 Oct 2014 15:00:28 +0300 Message-ID: <20141015120028.GG26918@redhat.com> References: <1413357930-45302-1-git-send-email-jasowang@redhat.com> <1413357930-45302-4-git-send-email-jasowang@redhat.com> <20141015093739.GC25776@redhat.com> <063D6719AE5E284EB5DD2968C1650D6D1C9D752A@AcuExch.aculab.com> <20141015104806.GK25776@redhat.com> <063D6719AE5E284EB5DD2968C1650D6D1C9D7688@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: "eric.dumazet@gmail.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "davem@davemloft.net" To: David Laight Return-path: Content-Disposition: inline In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1C9D7688@AcuExch.aculab.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org On Wed, Oct 15, 2014 at 10:51:32AM +0000, David Laight wrote: > From: Michael S. Tsirkin > > On Wed, Oct 15, 2014 at 09:49:01AM +0000, David Laight wrote: > > > From: Of Michael S. Tsirkin > > > > On Wed, Oct 15, 2014 at 03:25:27PM +0800, Jason Wang wrote: > > > > > Accumulate the sent packets and sent bytes in local variables and perform a > > > > > single u64_stats_update_begin/end() after. > > > > > > > > > > Cc: Rusty Russell > > > > > Cc: Michael S. Tsirkin > > > > > Signed-off-by: Jason Wang > > > > > > > > Not sure how much it's worth but since Eric suggested it ... > > > > > > Probably depends on the actual cost of u64_stats_update_begin/end > > > against the likely extra saving of the tx_bytes and tx_packets > > > values onto the stack across the call to dev_kfree_skb_any(). > > > (Which depends on the number of caller saved registers.) > > > > Yea, some benchmark results would be nice to see. > > I there are likely to be multiple skb on the queue the fastest > code would probably do one 'virtqueue_get_all()' that returned > a linked list of buffers, then follow the list to get the stats, > and follow it again to free the skb. > > David Interesting. Each time we tried playing with linked list in the past, it simply destroyed performance. Maybe this case is different but I have my doubts. > > > > Acked-by: Michael S. Tsirkin > > > > > > > > > --- > > > > > drivers/net/virtio_net.c | 12 ++++++++---- > > > > > 1 files changed, 8 insertions(+), 4 deletions(-) > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > index 3d0ce44..a4d56b8 100644 > > > > > --- a/drivers/net/virtio_net.c > > > > > +++ b/drivers/net/virtio_net.c > > > > > @@ -833,17 +833,21 @@ static void free_old_xmit_skbs(struct send_queue *sq) > > > > > unsigned int len; > > > > > struct virtnet_info *vi = sq->vq->vdev->priv; > > > > > struct virtnet_stats *stats = this_cpu_ptr(vi->stats); > > > > > + u64 tx_bytes = 0, tx_packets = 0; > > > > > > tx_packets need only be 'unsigned int'. > > > The same is almost certainly true of tx_bytes. > > > > > > David > > > > > > > > while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) { > > > > > pr_debug("Sent skb %p\n", skb); > > > > > > > > > > - u64_stats_update_begin(&stats->tx_syncp); > > > > > - stats->tx_bytes += skb->len; > > > > > - stats->tx_packets++; > > > > > - u64_stats_update_end(&stats->tx_syncp); > > > > > + tx_bytes += skb->len; > > > > > + tx_packets++; > > > > > > > > > > dev_kfree_skb_any(skb); > > > > > } > > > > > + > > > > > + u64_stats_update_begin(&stats->tx_syncp); > > > > > + stats->tx_bytes += tx_bytes; > > > > > + stats->tx_packets =+ tx_packets; > > > > > + u64_stats_update_end(&stats->tx_syncp); > > > > > } > > > > > > > > > > static int xmit_skb(struct send_queue *sq, struct sk_buff *skb) > > > > > -- > > > > > 1.7.1 > > > > -- > > > > To unsubscribe from this list: send the line "unsubscribe netdev" in > > > > the body of a message to majordomo@vger.kernel.org > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > >