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Date: Thu, 1 Dec 2016 13:47:29 -0800
From: Rick Jones <rick.jones2@....com>
To: Tom Herbert <tom@...bertland.com>
Cc: Sowmini Varadhan <sowmini.varadhan@...cle.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Initial thoughts on TXDP
On 12/01/2016 12:18 PM, Tom Herbert wrote:
> On Thu, Dec 1, 2016 at 11:48 AM, Rick Jones <rick.jones2@....com> wrote:
>> Just how much per-packet path-length are you thinking will go away under the
>> likes of TXDP? It is admittedly "just" netperf but losing TSO/GSO does some
>> non-trivial things to effective overhead (service demand) and so throughput:
>>
> For plain in order TCP packets I believe we should be able process
> each packet at nearly same speed as GRO. Most of the protocol
> processing we do between GRO and the stack are the same, the
> differences are that we need to do a connection lookup in the stack
> path (note we now do this is UDP GRO and that hasn't show up as a
> major hit). We also need to consider enqueue/dequeue on the socket
> which is a major reason to try for lockless sockets in this instance.
So waving hands a bit, and taking the service demand for the GRO-on
receive test in my previous message (860 ns/KB), that would be ~
(1448/1024)*860 or ~1.216 usec of CPU time per TCP segment, including
ACK generation which unless an explicit ACK-avoidance heuristic a la
HP-UX 11/Solaris 2 is put in place would be for every-other segment. Etc
etc.
> Sure, but trying running something emulates a more realistic workload
> than a TCP stream, like RR test with relative small payload and many
> connections.
That is a good point, which of course is why the RR tests are there in
netperf :) Don't get me wrong, I *like* seeing path-length reductions.
What would you posit is a relatively small payload? The promotion of
IR10 suggests that perhaps 14KB or so is a sufficiently common so I'll
grasp at that as the length of a piece of string:
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,14K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 14336 10.00 8118.31 1.57 -1.00 46.410 -1.000
16384 87380
stack@...cp1-c0-m1-mgmt:~/rjones2$ sudo ethtool -K hed0 gro off
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,14K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 14336 10.00 5837.35 2.20 -1.00 90.628 -1.000
16384 87380
So, losing GRO doubled the service demand. I suppose I could see
cutting path-length in half based on the things you listed which would
be bypassed?
I'm sure mileage will vary with different NICs and CPUs. The ones used
here happened to be to hand.
happy benchmarking,
rick
Just to get a crude feel for sensitivity, doubling to 28K unsurprisingly
goes to more than doubling, and halving to 7K narrows the delta:
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,28K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 28672 10.00 6732.32 1.79 -1.00 63.819 -1.000
16384 87380
stack@...cp1-c0-m1-mgmt:~/rjones2$ sudo ethtool -K hed0 gro off
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,28K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 28672 10.00 3780.47 2.32 -1.00 147.280 -1.000
16384 87380
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,7K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 7168 10.00 10535.01 1.52 -1.00 34.664 -1.000
16384 87380
stack@...cp1-c0-m1-mgmt:~/rjones2$ sudo ethtool -K hed0 gro off
stack@...cp1-c0-m1-mgmt:~/rjones2$ ./netperf -c -H np-cp1-c1-m3-mgmt -t
TCP_RR -- -P 12867 -r 128,7K
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 12867
AF_INET to np-cp1-c1-m3-mgmt () port 12867 AF_INET : demo : first burst 0
Local /Remote
Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
Send Recv Size Size Time Rate local remote local remote
bytes bytes bytes bytes secs. per sec % S % U us/Tr us/Tr
16384 87380 128 7168 10.00 8225.17 1.80 -1.00 52.661 -1.000
16384 87380
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