Subject: Re: [linux-audio-dev] Re: high level laaga
From: Abramo Bagnara (abramo_AT_alsa-project.org)
Date: Fri May 11 2001 - 23:14:41 EEST
Abramo Bagnara wrote:
>
> However if I interpret right the web page:
>
> "The benchmark times how long it takes to go from one process to another
> when the context switch is done by reading and writing data."
>
> Then I suppose this is not the pure context switch time, but it's
> cumulated with read/write syscall and copy time that seems to be
> significative. Note also that in current kernel code pipe needs a double
> copy (Manfred Spraul is improving that in recent past days).
>
> If (I underline "if") the cost is ~2 microseconds this means 0.1538% of
> CPU use per context switch.
>
> Do you think I'm missing something?
>
> I'll try to do some tests here (with a k6 II @ 333Mhz: a little machine)
> using sched_yield and rdtsc. Probably I can obtain more data.
I attach my test program (don't try it on SMP).
Results are very interesting:
$ cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 5
model : 8
model name : AMD-K6(tm) 3D processor
stepping : 0
cpu MHz : 333.113
cache size : 64 KB
fdiv_bug : no
hlt_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 mmx syscall 3dnow
bogomips : 663.55
$ cat /proc/version
Linux version 2.4.4 (root_AT_igor) (gcc version 2.96 20000731 (Red Hat
Linux 7.1 2.96-81)) #5 SMP sab mag 5 19:00:39 CEST 2001
$ ./ctx 2
0: 499998 iterations
1: 500002 iterations
min=893 max=397782 avg=918
$ ./ctx 2
0: 499992 iterations
1: 500008 iterations
min=886 max=85798 avg=917
$ ./ctx 2
0: 499997 iterations
1: 500003 iterations
min=893 max=85635 avg=918
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1000000000*918/333113000
2755
Average time for a context switch:
2755ns = 2.755us
Another machine:
$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 8
model name : Pentium III (Coppermine)
stepping : 6
cpu MHz : 797.995
cache size : 256 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 sep mtrr pge mca
cmov pat pse36 mmx fxsr sse
bogomips : 1592.52
$ cat /proc/version
Linux version 2.4.4-xfs (root_AT_linux1) (gcc version 2.96 20000731 (Red
Hat Linux 7.1 2.96-84)) #12 mer mag 9 11:47:14 CEST 2001
$ ./ctx 2
0: 499999 iterations
1: 500001 iterations
min=556 max=57779 avg=570
$ ./ctx 2
0: 499999 iterations
1: 500001 iterations
min=556 max=42148 avg=570
$ ./ctx 2
0: 500001 iterations
1: 499999 iterations
min=559 max=183607 avg=571
$ bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1000000000*571/797995000
715
Average time for a context switch:
715ns = 0.715us
I don't know if to use fork would change significatively this numbers.
-- Abramo Bagnara mailto:abramo_AT_alsa-project.orgOpera Unica Phone: +39.546.656023 Via Emilia Interna, 140 48014 Castel Bolognese (RA) - Italy
ALSA project http://www.alsa-project.org It sounds good!
This archive was generated by hypermail 2b28 : Fri May 11 2001 - 23:30:43 EEST