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SubjectRe: [patch] e1000 TSO parameter
[Scott, somehow I never received your original response so I'm
replying based on what I saw in the linux.kernel newgroup...]

Scott> Do you have any data to share?

Sure, I don't see why not. Here are the number I got:

TSO disabled:

$ modprobe InterruptThrottleRate=0,0,0,0 TSO=0,0,0,0
$ netperf -l 30 -c -C -H foobar -- -s64K -S64K
TCP STREAM TEST to foobar
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

131070 131072 131072 30.00 897.16 34.07 35.00 3.111 3.196

TSO enabled:

$ modprobe InterruptThrottleRate=0,0,0,0 TSO=1,1,1,1
$ netperf -l 30 -c -C -H foobar -- -s64K -S64K
TCP STREAM TEST to foobar
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

131070 131072 131072 30.00 894.09 11.65 34.48 1.068 3.159

This looks roughly like you'd expect: with TSO, slightly lower
throughput but much less CPU overhead.

With ftp, things get stranger: fetching a 2GByte file via ftp get
(from the remote end):

TSO disabled:

ftp> get big.iso /dev/null
local: /dev/null remote: big.iso
200 PORT command successful.
150 Opening BINARY mode data connection for 'big.iso' (2038628352 bytes).
226 Transfer complete.
2038628352 bytes received in 18.17 secs (109554.5 kB/s)

ftp server CPU utilization: ~ 40%

With TSO enabled:

ftp> get big.iso /dev/null
local: /dev/null remote: big.iso
200 PORT command successful.
150 Opening BINARY mode data connection for 'big.iso' (2038628352 bytes).
226 Transfer complete.
2038628352 bytes received in 21.16 secs (94070.2 kB/s)

ftp server CPU utilization: ~ 15%

So we get almost 15% of throughput drop. This was with plain "netkit
fptd". AFAIK, it does a simple read/write loop (not sendfile()).

--david
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