Messages in this thread Patches in this message | | | Date | Wed, 1 Dec 2021 15:32:36 +0000 | Subject | Re: [RFC 00/12] io_uring zerocopy send | From | Pavel Begunkov <> |
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On 12/1/21 03:10, David Ahern wrote: > On 11/30/21 8:18 AM, Pavel Begunkov wrote: >> Early proof of concept for zerocopy send via io_uring. This is just >> an RFC, there are details yet to be figured out, but hope to gather >> some feedback. >> >> Benchmarking udp (65435 bytes) with a dummy net device (mtu=0xffff): >> The best case io_uring=116079 MB/s vs msg_zerocopy=47421 MB/s, >> or 2.44 times faster. >> >> № | test: | BW (MB/s) | speedup >> 1 | msg_zerocopy (non-zc) | 18281 | 0.38 >> 2 | msg_zerocopy -z (baseline) | 47421 | 1 >> 3 | io_uring (@flush=false, nr_reqs=1) | 96534 | 2.03 >> 4 | io_uring (@flush=true, nr_reqs=1) | 89310 | 1.88 >> 5 | io_uring (@flush=false, nr_reqs=8) | 116079 | 2.44 >> 6 | io_uring (@flush=true, nr_reqs=8) | 109722 | 2.31 >> >> Based on selftests/.../msg_zerocopy but more limited. You can use >> msg_zerocopy -r as usual for receive side. >> > ... > > Can you state the exact command lines you are running for all of the > commands? I tried this set (and commands referenced below) and my
Sure. First, for dummy I set mtu by hand, not sure can do it from the userspace, can I? Without it __ip_append_data() falls into non-zerocopy path.
diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c index f82ad7419508..5c5aeacdabd5 100644 --- a/drivers/net/dummy.c +++ b/drivers/net/dummy.c @@ -132,7 +132,8 @@ static void dummy_setup(struct net_device *dev) eth_hw_addr_random(dev); dev->min_mtu = 0; - dev->max_mtu = 0; + dev->mtu = 0xffff; + dev->max_mtu = 0xffff; }
# dummy configuration
modprobe dummy numdummies=1 ip link set dummy0 up # force requests to <dummy_ip_addr> go through the dummy device ip route add <dummy_ip_addr> dev dummy0
With dummy I was just sinking the traffic to the dummy device, was good enough for me. Omitting "taskset" and "nice":
send-zc -4 -D <dummy_ip_addr> -t 10 udp
Similarly with msg_zerocopy:
<kernel>/tools/testing/selftests/net/msg_zerocopy -4 -p 6666 -D <dummy_ip_addr> -t 10 -z udp
For loopback testing, as zerocopy is not allowed for it as Willem explained in the original MSG_ZEROCOPY cover-letter, I used a hack to bypass it:
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index ebb12a7d386d..42df33b175ce 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2854,9 +2854,7 @@ static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask) /* Frags must be orphaned, even if refcounted, if skb might loop to rx path */ static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask) { - if (likely(!skb_zcopy(skb))) - return 0; - return skb_copy_ubufs(skb, gfp_mask); + return skb_orphan_frags(skb, gfp_mask); } /** Then running those two lines below in parallel and looking for the numbers send shows. It was in favor of io_uring for me, but don't remember exactly. perf shows that "send-zc" spends lot of time receiving, so wasn't testing performance of it after some point.
msg_zerocopy -r -v -4 -t 20 udp send-zc -4 -D 127.0.0.1 -t 10 udp
> mileage varies quite a bit.
Interesting, any brief notes on the setup and the results? Dummy or something real? io_uring doesn't show if it was really zerocopied or not, but I assume you checked it (e.g. with perf/bpftrace).
I expected that @flush=true might be worse with real devices, there is one spot to be patched, but apart from that and cycles spend in a real LLD offseting the overhead, didn't anticipate any problems. I'll see once I try a real device.
> Also, have you run this proposed change (and with TCP) across nodes > (ie., not just local process to local process via dummy interface)?
Not yet, I tried dummy, and localhost UDP as per above and similarly TCP. Just need to grab a server with a proper NIC, will try it out soon.
>> Benchmark: >> https://github.com/isilence/liburing.git zc_v1 >> >> or this file in particular: >> https://github.com/isilence/liburing/blob/zc_v1/test/send-zc.c >> >> To run the benchmark: >> ``` >> cd <liburing_dir> && make && cd test >> # ./send-zc -4 [-p <port>] [-s <payload_size>] -D <destination> udp >> ./send-zc -4 -D 127.0.0.1 udp >> ``` >> >> msg_zerocopy can be used for the server side, e.g. >> ``` >> cd <linux-kernel>/tools/testing/selftests/net && make >> ./msg_zerocopy -4 -r [-p <port>] [-t <sec>] udp >> ```
-- Pavel Begunkov
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