CPU pinning

[Kernel Piddu]

Thanks so much for the detailed info. It's very comprehensive. Thanks for taking the time.

On Sep 26, 2011, at 6:51 AM, Peter Teoh <htmldeveloper at gmail.com> wrote:

> On Fri, Sep 16, 2011 at 5:08 AM, Kernel Piddu <kernelpiddu at gmail.com> wrote:
>> 
>>> I have a multi processor system/machine and I would like dedicate a CPU entirely to listen on to a port.
>>> I would greatly appreciate if you could tell me how this can be done.
>>> 
>>> Thanks!
>> 
> 
> doing this in the kernel, is perhaps not really recommended, and linux
> kernel is become UNIX-non-compliant if such features were ever
> provided.
> but userspace, is definitely possible, but is always a suggestive
> tuning....the kernel can always override your request:
> http://www.cyberciti.biz/tips/setting-processor-affinity-certain-task-or-process.html
> but this is per-process, if u want per-port IRQ handling attach to the
> core, then this is going to affect the algorithm kernel used for
> SoftIRQ handling:
> 
> doing a "cat /proc/softirqs" on my system:
> 
>                 CPU0       CPU1       CPU2       CPU3
>       HI:          0          0          0          0
>    TIMER:     563854     591025          0          0
>   NET_TX:          7          6          0          0
>   NET_RX:      17486      19250          0          0
>    BLOCK:      28888       3784          0          0
> BLOCK_IOPOLL:          0          0          0          0
>  TASKLET:     399230     391008          0          0
>    SCHED:     116858     119604          0          0
>  HRTIMER:        978        610          0          0
>      RCU:     158513     192567          0          0
> 
> i can see that the IRQ processing is skewed, but then unless i have an
> overall picture of what every core is doing.....not advisable to touch
> that.
> 
> anyway looking at the "processes":
> 
> root         3     2  0 16:59 ?        00:00:00 [ksoftirqd/0]
> root         7     2  0 16:59 ?        00:00:00 [ksoftirqd/1]
> 
> only two tasklet thread are spawned to handle the these softirq at
> each core.   i suspect some error in the interpreting the number of
> cores here, as there is only two core. (/proc/cpuinfo).
> 
> good reading on these internals:
> 
> http://lwn.net/Articles/308117/
> http://www.wil.cx/matthew/lca2003/paper.pdf
> 
> --
> Regards,
> Peter Teoh