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SubjectPROBLEM: select() on TCP socket sleeps for 1 tick even if data available
[1.] select() sleeps for 1 tick even if data available
[2.] Full description of the problem/report:
If select() is waiting for data to become available on a TCP socket FD,
and
data becomes available, it doesn't return until the next clock tick.
This
produces large latencies when passing data between processes several
times,
since each transaction (which requires microseconds) does not occur
until
the next clock tick, limiting the entire throughput of the system to
100
transactions/second.
[3.] Keywords: select, socket, networking
[4.] Kernel version (from /proc/version): 2.2.18
[5.] Output of Oops.. message (not applicable)
[6.] A small shell script or example program which triggers the
problem (if possible)

#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

/* this program should take 1 second to complete, but takes 10 */
/* yes i know, it doesn't do any I/O, but the behavior is the
same as if it did */
main()
{
for (int i = 0; i < 1000; i++) {
struct timeval to;
to.tv_sec = 0;
to.tv_usec = 1000;
select(0, 0, 0, 0, &to);
}
return 0;
}

[7.] Environment
Red Hat 7.0 with kernel upgraded to 2.2.18

[7.1.] Software (add the output of the ver_linux script here)
ver_linux di dnot appear to work. However, here's its output.

Linux mlindner-ras.sonusnet.com 2.2.18 #8 Wed Jan 3 01:40:29 EST 2001
i586 unknown
Kernel modules found
Gnu C 2.96
Binutils 2.10.0.18
Linux C Library ..
ldd: missing file arguments
Try `ldd --help' for more information.
ls: /usr/lib/libg++.so: No such file or directory
Procps 2.0.7
Mount 2.10m
Net-tools (2000-05-21)
Kbd [option...]
Sh-utils 2.0
Sh-utils Parker.
Sh-utils
Sh-utils Inc.
Sh-utils NO
Sh-utils PURPOSE.

[7.2.] Processor information (from /proc/cpuinfo):

processor : 0
vendor_id : AuthenticAMD
cpu family : 5
model : 8
model name : AMD-K6(tm) 3D processor
stepping : 12
cpu MHz : 451.033
cache size : 64 KB
fdiv_bug : no
hlt_bug : no
sep_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr mce cx8 sep mtrr pge mmx 3dnow
bogomips : 897.84

[7.3.] Module information (from /proc/modules): N/A
[7.4.] SCSI information (from /proc/scsi/scsi) N/A
[7.5.] Other information that might be relevant to the problem
(please look in /proc and include all information that you
think to be relevant):
[X.] Other notes, patches, fixes, workarounds:

--
Mike Lindner
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