Hi,

We are dealing with an application that is a fairly heavy user of
POSIX message queues. While running this application I seemed to have
stumbled upon the fact that the timeout in the mq_timedrecieve is
innaccurate to the tune of a more than 5-6 miliseconds and that it is
fairly consistent even at its highest priority.

Cyclictest on the same machine gives me a max deviation of about 7uS,
so I guess my timers (hrt) are functioning alright.

Here is a small program I hacked up from the LTP sources to
demonstrate this behaviour (attached). I ran this on a dual core
2.5Ghz cpu and a uniprocessor 1.5Ghz cpu (cpuinfo below). On the
dual-core I can see that its off by 1-2 miliseconds but on the 1.5 Ghz
celeron its off by 6-8 miliseconds sometimes.

kernel version: 2.6.33.1-rt10

Usage: ./send_rev_2 <timeout_in_miliseconds>

$ cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 13
model name      : Intel(R) Celeron(R) M processor         1.50GHz
stepping        : 8
cpu MHz         : 1500.111
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
clflush dts acpi mmx fxsr sse sse2 ss tm pbe nx up bts

Also attaached is my .config.

thanks in advance
regards
/prady


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