Re: [PATCH] bitmap, irq: Add smp_affinity_list interface to /proc/irq

[Mike Travis]

Andrew Morton wrote:
> On Tue, 29 Mar 2011 16:56:12 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Tue, 29 Mar 2011 16:46:52 -0700
> > Mike Travis <travis@xxxxxxx> wrote:
> >
> > > +	/* create /proc/irq/<irq>/smp_affinity_list */
> > > +	proc_create_data("smp_affinity_list", 0600, desc->dir,
> > > +			 &irq_affinity_list_proc_fops, (void *)(long)irq);
> > Always document your interfaces, please.  `grep -r smp_affinity
> > Documentation' shows where.
> >
> > And one we've seen a description of the proposed new interface, we can
> > review the patch!
>
> Also, the patch adds a new interface which duplicates an existing one,
> only the formats are different, yes?  This is, of course, bad.
>
> The only justification we've seen for being bad is "Manually adjusting
> the smp_affinity for IRQ's becomes unwieldy when the cpu count is
> large".  A more thorough description of how painful this is might help
> motivate people to do bad things to the kernel.
>
> Also, if it's just a matter of an alternative presentation of the data,
> why not implement the desired user interface with a little userspace
> tool then feed the results down into the existing kernel interface?

Setting smp affinity to cpus 256 to 263 would be:

echo 000000ff,00000000,00000000,00000000,00000000,00000000,00000000,00000000 > smp_affinity

instead of:

echo 256-263 > smp_affinity_list

Think about what it looks like for cpus around say, 4088 to 4095.

We already have many alternate "list" interfaces:

/sys/devices/system/cpu/cpuX/indexY/shared_cpu_list
/sys/devices/system/cpu/cpuX/topology/thread_siblings_list
/sys/devices/system/cpu/cpuX/topology/core_siblings_list
/sys/devices/system/node/nodeX/cpulist
/sys/devices/pci***/***/local_cpulist

etc.

This just expands on that same philosophy.

Thanks,
Mike
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