is irq smp affinity good for anything?

[uaca@alumni.uv.es]

if IRQ affinity cannot help in interrupt latency and
interrupt auto/balancing get's the same throughtput 
as irq binding... what is irq smp affinity for???

from this mail from intel
http://www.uwsg.iu.edu/hypermail/linux/kernel/0301.0/1886.html
I understand that intel's interrupt auto/balancing works equal that manually
tunning the interrupts....

so?

	Ulisses



On Mon, Mar 10, 2003 at 11:22:22PM +0100, uaca@alumni.uv.es wrote:
> 
> Hi all
> 
> I have measured interrupt latency of a bi-processor system with akpm's intlat/timepeg
> utilities and kernel 2.4.20. The system uses is a two-way PIII@800Mhz
> -- Intel motherboard, ISP 2100 if I remember ok, with a SCSI disk on a aic-7896
> 
> I tried to know if I could reduce the latency of an interrupt handler by
> binding this handler to a particular cpu and not allowing any other
> interrupt to execute in that cpu.
> 
> I found that overall latency increases, but also the latency on both cpus,
> that is, I could not reduce the latency on the interrupt I was interested
> 
> I also tried to disallowing just scsi & ethernet handlers to execute on the
> cpu in wich I'm binding the interrupt handler I'm insterested with, I get
> similar results
> 
> the interrupt handler I'm interested with is an ATM card receiving
> around 6000 interrupts/second
> 
> any comment will be greatly appreciated
> 
> Thanks in advance
> 
> 
> I attach a sample table
> 
> 	Ulisses
> 
>                 Debian GNU/Linux: a dream come true
> -----------------------------------------------------------------------------
> "Computers are useless. They can only give answers."            Pablo Picasso
> 
> --->	Visita http://www.valux.org/ para saber acerca de la	<---
> --->	Asociación Valenciana de Usuarios de Linux		<---
> 
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> 
> bound-*      -> binding irq's to specific cpu's
> not_bound-*  -> default irq balancing
> idle-*       -> no extra load, just receiving interrupts, and using irq balancing 
>                 (not tcpdumping from the device)
> 
> *-round?     -> same test, just another sample
> 
> The following loads were added:
> 
> */cpu_io_load* -> adding a process load, and another process doing intensive I/O (write) +tcpdump
> */cpu_load*    -> process load +tcpdump
> */io_load*     -> I/O load +tcpdump
> */no_load*     -> just tcpdump (always running on the ATM card)
> 
> time unit is microseconds
> 
> <config name>                                <cpu0>      <cpu1>     <both cpu>   <running time>
> bound-round1/cpu_io_load.conf-capturando-atm 72721403.12 32011026.4 104732430.03 334000000
> bound-round1/cpu_load.conf-capturando-atm 17330835.03 22209536.73 39540372.14 301000000
> bound-round1/io_load.conf-capturando-atm 26490926.85 35473241.13 61964168.45 332000000
> bound-round1/no_load.conf-capturando-atm 17723058.55 24066995.44 41790054.28 300000000
> bound-round2/cpu_io_load.conf-capturando-atm 70139325.9899999 31673560.18 101812886.64 332000000
> bound-round2/cpu_load.conf-capturando-atm 20834850.44 22103680.54 42938531.31 300000000
> bound-round2/io_load.conf-capturando-atm 25995860.86 35030250.99 61026112.51 331000000
> bound-round2/no_load.conf-capturando-atm 16926317.67 22890716.86 39817034.87 300000000
> not_bound-round1/cpu_io_load.conf-capturando-atm 27857114.18 30214652.36 58071767.23 330000000
> not_bound-round1/cpu_load.conf-capturando-atm 17861389.71 17826837.68 35688227.83 300000000
> not_bound-round1/io_load.conf-capturando-atm 28921009.86 30368027.35 59289037.74 329000000
> not_bound-round1/no_load.conf-capturando-atm 17095881.6 17804144.4 34900026.4 301000000
> not_bound-round2/cpu_io_load.conf-capturando-atm 28958809.19 29576235.94 58535045.78 333000000
> not_bound-round2/cpu_load.conf-capturando-atm 17654701.15 19004883.19 36659584.82 301000000
> not_bound-round2/io_load.conf-capturando-atm 30383447.95 31634551.35 62017999.99 332000000
> not_bound-round2/no_load.conf-capturando-atm 18103003.63 17573932.55 35676936.69 300000000
> idle-round1/no_load.conf-idle 0 0 16030718.21 300000000
> idle-round2/no_load.conf-idle 0 0 16106698.44 300000000
> -
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-- 
                Debian GNU/Linux: a dream come true
-----------------------------------------------------------------------------
"Computers are useless. They can only give answers."            Pablo Picasso

--->	Visita http://www.valux.org/ para saber acerca de la	<---
--->	Asociación Valenciana de Usuarios de Linux		<---