Yep, other OS's dont behave the same. However:
On doing a man 7 socket:
NOTES
Linux assumes that half of the send/receive buffer is used
for internal kernel structures; thus the sysctls are twice
than what can be observed on the wire.
Linux does double the buffer size:
case SO_SNDBUF:
/* Don't error on this BSD doesn't and if you think
about it this is right. Otherwise apps have to
play 'guess the biggest size' games. RCVBUF/SNDBUF
are treated in BSD as hints */
if (val > sysctl_wmem_max)
val = sysctl_wmem_max;
sk->userlocks |= SOCK_SNDBUF_LOCK;
sk->sndbuf = max(val*2,SOCK_MIN_SNDBUF);
/*
* Wake up sending tasks if we
* upped the value.
*/
sk->write_space(sk);
break;
Previous discussions on this topic:
http://www.uwsg.indiana.edu/hypermail/linux/kernel/0004.2/1054.html
While this isnt reflective of a very slow link, I see the following
on a 100Mb lan, 2.4.2 kernel, between a 400MHz and a 866Mhz uniproc:
Actual
Socket Sizes Message Size Thruput Confidence
(snd = rcv) (bytes) (Mb/s) % # iters
----------- ------------ ------- ----------
2048 64 23.99 99 15
4096 64 30.30 99 15
8192 64 90.12 99 15
12288 64 89.90 99 15
16384 64 93.11 99 15
20480 64 92.00 99 15
24576 64 93.33 99 15
28672 64 93.33 99 15
32768 64 93.74 99 15
40960 64 93.87 99 15
49152 64 93.91 99 15
57344 64 93.92 99 15
65536 64 93.99 99 15
81920 64 92.24 99 15
98304 64 94.06 99 15
114688 64 93.46 99 15
131072 64 93.43 99 15
131072 64 93.50 99 15
Actual
Socket Sizes Message Size Thruput Confidence
(snd = rcv) (bytes) (Mb/s) % # iters
----------- ------------ ------- ----------
2048 4096 44.23 99 15
4096 4096 57.47 99 15
8192 4096 70.29 99 15
12288 4096 91.90 99 15
16384 4096 93.81 99 15
20480 4096 92.68 99 15
24576 4096 93.68 99 15
28672 4096 93.68 99 15
32768 4096 93.76 99 15
40960 4096 94.05 99 15
49152 4096 94.00 99 15
57344 4096 93.99 99 15
65536 4096 94.02 99 15
81920 4096 93.61 99 15
98304 4096 94.08 99 15
114688 4096 93.80 99 15
131072 4096 93.76 99 15
131072 4096 93.74 99 15
Actual
Socket Sizes Message Size Thruput Confidence
(snd = rcv) (bytes) (Mb/s) % # iters
----------- ------------ ------- ----------
2048 32768 46.64 99 15
4096 32768 59.62 99 15
8192 32768 70.82 99 15
12288 32768 91.67 99 15
16384 32768 93.85 99 15
20480 32768 92.52 99 15
24576 32768 94.04 99 15
28672 32768 94.04 99 15
32768 32768 93.93 99 15
40960 32768 94.06 99 15
49152 32768 94.07 99 15
57344 32768 94.06 99 15
65536 32768 94.08 99 15
81920 32768 93.37 99 15
98304 32768 93.69 99 15
114688 32768 93.77 99 15
131072 32768 93.88 99 15
131072 32768 93.78 99 15
thanks,
nivedita
-
: send the line "unsubscribe linux-net" in
the body of a message to majordomo@vger.kernel.org
