linux-kernel - Re: [PATCH] bitmap, irq: Add smp_affinity

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Message-Id: <20110329175614.0c41ae8c.akpm@linux-foundation.org>
Date:	Tue, 29 Mar 2011 17:56:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Travis <travis@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jack Steiner <steiner@....com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bitmap, irq: Add smp_affinity_list interface to
 /proc/irq

On Tue, 29 Mar 2011 17:51:18 -0700 Mike Travis <travis@....com> 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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