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

[Mike Travis]

Andrew Morton wrote:
> On Tue, 29 Mar 2011 17:51:18 -0700 Mike Travis <travis@xxxxxxx> wrote:
>
> > > 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.
>
> You mean that if someone had written a stupid little tool to convert a
> list of tuples into a bitmap, we wouldn't have needed to add all that
> crap to the kernel?
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