Re: all syscalls initially taking 4usec on a P4? Re: nonblocking UDPv4 recvfrom() taking 4usec @ 3GHz?

Stephen Hemminger
2007-02-20T21:02:58Z

On Tue, 20 Feb 2007 21:45:05 +0100
bert hubert <bert.hubert@netherlabs.nl> wrote:

> On Tue, Feb 20, 2007 at 02:40:40PM -0500, Benjamin LaHaise wrote:
>
> > Make sure your system is idle. Userspace bloat means that *lots* of idle
> > activity occurs in between timer ticks on recent distributions -- all those
>
> You hit the nail on the head. I had previously measured with X shut down,
> but the effect didn't disappear.
>
> With init=/bin/bash, recvfrom suddenly takes from 900nsec to 1.3usec, with
> only slight correlation between inter-call delay and cycles spent.
>
> I'm investigating this further as it appears this has a real life effect on
> my P4 - a drastic one!
>
> processor : 0
> vendor_id : GenuineIntel
> cpu family : 15
> model : 4
> model name : Intel(R) Pentium(R) 4 CPU 3.00GHz
> stepping : 1
> cpu MHz : 3000.131
> cache size : 1024 KB
> fdiv_bug : no
> hlt_bug : no
> f00f_bug : no
> coma_bug : no
> fpu : yes
> fpu_exception : yes
> cpuid level : 5
> wp : yes
> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx
> constant_tsc pni monitor ds_cpl cid xtpr
> bogomips : 6003.91
> clflush size : 64
>
> Thanks for your help!
>

What happens with preempt if your process is high priority or SCHED_FIFO/SCHED_RR?

--
Stephen Hemminger <shemminger@linux-foundation.org>