Re: PROBLEM: select() on TCP socket sleeps for 1 tick even if data available

["Stephen D. Williams" <sdw@lig.net>]

An old thread, but important to get these fundamental performance
numbers up there:

2.4.2 on an 800mhz PIII Sceptre laptop w/ 512MB ram:

elapsed time for 100000 pingpongs is
3.81327                                    
100000/3.81256
        ~26229.09541095746689888159     
10000/.379912
        ~26321.88506812103855629724  

26300 compares to 8000/sec. quite well ;-)  You didn't give specs for
your test machine unfortunately.

Since this tests both 'sides' of an application communication, it
indicates a 'null transaction' rate of twice that.

This was typical cpu usage on a triple run of 10000:
CPU states:  7.2% user, 92.7% system,  0.0% nice,  0.0% idle  

sdw


Michael Lindner wrote:
> 
> OK, 2.4.0 kernel installed, and a new set of numbers:
> 
> test            kernel          ping-pongs/s. @ total CPU util  w/SOL_NDELAY
> sample (2 skts) 2.2.18          100 @ 0.1%                      800 @ 1%
> sample (1 skt)  2.2.18          8000 @ 100%                     8000 @ 50%
> real app        2.2.18          100 @ 0.1%                      800 @ 1%
> 
> sample (2 skts) 2.4.0           8000 @ 50%                      8000 @ 50%
> sample (1 skt)  2.4.0           10000 @ 50%                     10000 @ 50%
> real app        2.4.0           1200 @ 50%                      1200 @ 50%
> 
> real app        Windows 2K      4000 @ 100%
> 
> The two points that still seem strange to me are:
> 
> 1. The 1 socket case is still 25% faster than the 2 socket case in 2.4.0
> (in 2.2.18 the 1 socket case was 10x faster).
> 
> 2. Linux never devotes more than 50% of the CPU (average over a long
> run) to the two processes (25% to each process, with the rest of the
> time idle).
> 
> I'd really love to show that Linux is a viable platform for our SW, and
> I think it would be doable if I could figure out how to get the other
> 50% of my CPU involved. An "strace -rT" of the real app on 2.4.0 looks
> like this for each ping/pong.
> 
>      0.052371 send(7, "\0\0\0
> \177\0\0\1\3243\0\0\0\2\4\236\216\341\0\0\v\277"..., 32, 0) = 32
> <0.000529>
>      0.000882 rt_sigprocmask(SIG_BLOCK, ~[], [RT_0], 8) = 0 <0.000021>
>      0.000242 rt_sigprocmask(SIG_SETMASK, [RT_0], NULL, 8) = 0
> <0.000021>
>      0.000173 select(8, [3 4 6 7], NULL, NULL, NULL) = 1 (in [6])
> <0.000047>
>      0.000328 read(6, "\0\0\0 ", 4)     = 4 <0.000031>
>      0.000179 read(6,
> "\177\0\0\1\3242\0\0\0\2\4\236\216\341\0\0\7\327\177\0\0"..., 28) = 28
> <0.000075>
> 
> --
> Mike Lindner
> -
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-- 
sdw@lig.net  http://sdw.st
Stephen D. Williams
43392 Wayside Cir,Ashburn,VA 20147-4622 703-724-0118W 703-995-0407Fax 
Dec2000