From: Rusty Russell <rusty@rustcorp.com.au> To: "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org Cc: Carsten Otte <cotte@de.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, linux390@de.ibm.com, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Shirley Ma <xma@us.ibm.com>, lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, Krishna Kumar <krkumar2@in.ibm.com>, Tom Lendacky <tahm@linux.vnet.ibm.com>, steved@us.ibm.com, habanero@linux.vnet.ibm.com Subject: Re: [PATCHv2 09/14] virtio_net: fix TX capacity checks using new API Date: Sat, 21 May 2011 11:43:19 +0930 [thread overview] Message-ID: <878vu0vm0w.fsf@rustcorp.com.au> (raw) In-Reply-To: <42ca2494c92f572388e3ab4c6f613dd4f038361b.1305846412.git.mst@redhat.com> On Fri, 20 May 2011 02:11:47 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote: > virtio net uses the number of sg entries to > check for TX ring capacity freed. But this > gives incorrect results when indirect buffers > are used. Use the new capacity API instead. OK, but this explanation needs enhancement, such as noting the actual results of that miscalculation. Something like: virtio_net uses the number of sg entries in the skb it frees to calculate how many descriptors in the ring have just been made available. But this value is an overestimate: with indirect buffers each skb only uses one descriptor entry, meaning we may wake the queue only to find we still can't transmit anything. Using the new virtqueue_get_capacity() call, we can exactly determine the remaining capacity, so we should use that instead. But, here's the side effect: > /* More just got used, free them then recheck. */ > - capacity += free_old_xmit_skbs(vi); > + free_old_xmit_skbs(vi); > + capacity = virtqueue_get_capacity(vi->svq); > if (capacity >= 2+MAX_SKB_FRAGS) { That capacity >= 2+MAX_SKB_FRAGS is too much for indirect buffers. This means we waste 20 entries in the ring, but OTOH if we hit OOM we fall back to direct buffers and we *will* need this. Which means this comment in the driver is now wrong: /* This can happen with OOM and indirect buffers. */ if (unlikely(capacity < 0)) { if (net_ratelimit()) { if (likely(capacity == -ENOMEM)) { dev_warn(&dev->dev, "TX queue failure: out of memory\n"); } else { dev->stats.tx_fifo_errors++; dev_warn(&dev->dev, "Unexpected TX queue failure: %d\n", capacity); } } dev->stats.tx_dropped++; kfree_skb(skb); return NETDEV_TX_OK; } virtqueue_kick(vi->svq); So I'm not applying this patch (nor the virtqueue_get_capacity predeccessor) for the moment. Thanks, Rusty.
WARNING: multiple messages have this Message-ID (diff)
From: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> To: "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: Krishna Kumar <krkumar2-xthvdsQ13ZrQT0dZR+AlfA@public.gmane.org>, Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, lguest-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Shirley Ma <xma-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, habanero-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org, Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, steved-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, Christian Borntraeger <borntraeger-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Tom Lendacky <tahm-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux390-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org Subject: Re: [PATCHv2 09/14] virtio_net: fix TX capacity checks using new API Date: Sat, 21 May 2011 11:43:19 +0930 [thread overview] Message-ID: <878vu0vm0w.fsf@rustcorp.com.au> (raw) In-Reply-To: <42ca2494c92f572388e3ab4c6f613dd4f038361b.1305846412.git.mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> On Fri, 20 May 2011 02:11:47 +0300, "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote: > virtio net uses the number of sg entries to > check for TX ring capacity freed. But this > gives incorrect results when indirect buffers > are used. Use the new capacity API instead. OK, but this explanation needs enhancement, such as noting the actual results of that miscalculation. Something like: virtio_net uses the number of sg entries in the skb it frees to calculate how many descriptors in the ring have just been made available. But this value is an overestimate: with indirect buffers each skb only uses one descriptor entry, meaning we may wake the queue only to find we still can't transmit anything. Using the new virtqueue_get_capacity() call, we can exactly determine the remaining capacity, so we should use that instead. But, here's the side effect: > /* More just got used, free them then recheck. */ > - capacity += free_old_xmit_skbs(vi); > + free_old_xmit_skbs(vi); > + capacity = virtqueue_get_capacity(vi->svq); > if (capacity >= 2+MAX_SKB_FRAGS) { That capacity >= 2+MAX_SKB_FRAGS is too much for indirect buffers. This means we waste 20 entries in the ring, but OTOH if we hit OOM we fall back to direct buffers and we *will* need this. Which means this comment in the driver is now wrong: /* This can happen with OOM and indirect buffers. */ if (unlikely(capacity < 0)) { if (net_ratelimit()) { if (likely(capacity == -ENOMEM)) { dev_warn(&dev->dev, "TX queue failure: out of memory\n"); } else { dev->stats.tx_fifo_errors++; dev_warn(&dev->dev, "Unexpected TX queue failure: %d\n", capacity); } } dev->stats.tx_dropped++; kfree_skb(skb); return NETDEV_TX_OK; } virtqueue_kick(vi->svq); So I'm not applying this patch (nor the virtqueue_get_capacity predeccessor) for the moment. Thanks, Rusty.
next prev parent reply other threads:[~2011-05-21 2:34 UTC|newest] Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-05-19 23:10 [PATCHv2 00/14] virtio and vhost-net performance enhancements Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 01/14] virtio: event index interface Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 02/14] virtio ring: inline function to check for events Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 03/14] virtio_ring: support event idx feature Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-19 23:10 ` [PATCHv2 04/14] vhost: support event index Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 05/14] virtio_test: " Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:32 ` Rusty Russell 2011-05-21 2:32 ` Rusty Russell 2011-05-21 2:32 ` Rusty Russell 2011-05-19 23:11 ` [PATCHv2 06/14] virtio: add api for delayed callbacks Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:33 ` Rusty Russell 2011-05-21 2:33 ` Rusty Russell 2011-05-21 2:33 ` Rusty Russell 2011-05-19 23:11 ` [PATCHv2 07/14] virtio_net: delay TX callbacks Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 08/14] virtio_ring: Add capacity check API Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 09/14] virtio_net: fix TX capacity checks using new API Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:13 ` Rusty Russell 2011-05-21 2:13 ` Rusty Russell [this message] 2011-05-21 2:13 ` Rusty Russell 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 10/14] virtio_net: limit xmit polling Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:19 ` Rusty Russell 2011-05-21 2:19 ` Rusty Russell 2011-05-21 2:19 ` Rusty Russell 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-23 2:07 ` Rusty Russell 2011-05-23 2:07 ` Rusty Russell 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-24 7:54 ` Krishna Kumar2 2011-05-24 7:54 ` Krishna Kumar2 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:27 ` Krishna Kumar2 2011-05-24 9:27 ` Krishna Kumar2 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 12:50 ` Krishna Kumar2 2011-05-24 12:50 ` Krishna Kumar2 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 12:50 ` Krishna Kumar2 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 7:54 ` Krishna Kumar2 2011-05-25 1:28 ` Rusty Russell 2011-05-25 1:28 ` Rusty Russell 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 1:28 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-26 3:28 ` Rusty Russell 2011-05-26 3:28 ` Rusty Russell 2011-05-26 3:28 ` Rusty Russell 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-30 6:27 ` Rusty Russell 2011-05-30 6:27 ` Rusty Russell 2011-05-30 6:27 ` Rusty Russell 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-23 2:07 ` Rusty Russell 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 11/14] virtio: don't delay avail index update Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-21 2:26 ` Rusty Russell 2011-05-21 2:26 ` Rusty Russell 2011-05-21 2:26 ` Rusty Russell 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 12/14] virtio: 64 bit features Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 13/14] virtio_test: update for " Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 14/14] vhost: fix " Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:20 ` [PATCHv2 00/14] virtio and vhost-net performance enhancements David Miller 2011-05-19 23:20 ` David Miller 2011-05-20 7:51 ` Rusty Russell 2011-05-20 7:51 ` Rusty Russell 2011-05-20 7:51 ` Rusty Russell 2011-05-26 15:32 ` [PERF RESULTS] " Krishna Kumar2 2011-05-26 15:32 ` Krishna Kumar2 2011-05-26 15:42 ` Shirley Ma 2011-05-26 16:21 ` Krishna Kumar2 2011-05-26 16:21 ` Krishna Kumar2 [not found] ` <OFF9D0E604.B865A006-ON6525789C.00597010-6525789C.0059987A@LocalDomain> 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 15:32 ` Krishna Kumar2
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