[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH net-next RFC 0/5] xen-netback: TX grant mapping instead of copy
On Wed, Oct 30, 2013 at 03:16:17PM -0400, Konrad Rzeszutek Wilk wrote: > On Wed, Oct 30, 2013 at 12:50:15AM +0000, Zoltan Kiss wrote: > > A long known problem of the upstream netback implementation that on the TX > > path (from guest to Dom0) it copies the whole packet from guest memory into > > Dom0. That simply became a bottleneck with 10Gb NICs, and generally it's a > > huge perfomance penalty. The classic kernel version of netback used grant > > mapping, and to get notified when the page can be unmapped, it used page > > destructors. Unfortunately that destructor is not an upstreamable solution. > > Ian Campbell's skb fragment destructor patch series > > (http://lwn.net/Articles/491522/) tried to solve this problem, however it > > seems to be very invasive on the network stack's code, and therefore haven't > > progressed very well. > > This patch series use SKBTX_DEV_ZEROCOPY flags to tell the stack it needs to > > know when the skb is freed up. That is the way KVM solved the same problem, > > and based on my initial tests it can do the same for us. Avoiding the extra > > copy boosted up TX throughput from 6.8 Gbps to 7.9 (I used a slower > > Interlagos box, both Dom0 and guest on upstream kernel, on the same NUMA > > node, > > running iperf 2.0.5, and the remote end was a bare metal box on the same > > 10Gb > > switch) > > Based on my investigations the packet get only copied if it is delivered to > > Dom0 stack, which is due to this patch: > > https://lkml.org/lkml/2012/7/20/363 > > That's a bit unfortunate, but as far as I know for the huge majority this > > use > > case is not too important. There are a couple of things which need more > > polishing, see the FIXME comments. I will run some more extensive tests, but > > in the meantime I would like to hear comments about what I've done so far. > > I've tried to broke it down to smaller patches, with mixed results, so I > > welcome suggestions on that part as well: > > 1/5: Introduce TX grant map definitions > > 2/5: Change TX path from grant copy to mapping > > 3/5: Remove old TX grant copy definitons > > 4/5: Fix indentations > > 5/5: Change RX path for mapped SKB fragments > > Odd. I don't see #5 patch patch? Ah, you have two #4 patches: [PATCH net-next RFC 4/5] xen-netback: Change RX path for mapped SKB fragments [PATCH net-next RFC 4/5] xen-netback: Fix indentations ! > > > > Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx> > > > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@xxxxxxxxxxxxx > > http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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