[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 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? > > 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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