linux-kernel - Re: [PATCH] [genirq] Expose default irq affinity mask (take 2)

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Date:	Thu, 29 May 2008 09:30:56 -0700
From:	Max Krasnyanskiy <maxk@...lcomm.com>
To:	Paul Jackson <pj@....com>
CC:	mingo@...e.hu, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	rdunlap@...otime.net
Subject: Re: [PATCH] [genirq] Expose default irq affinity mask (take 2)

Paul Jackson wrote:
> Review comments ... just nits ... patch looks good overall.
> 
> 1.  Trailing whitespace on Doc lines:
> 	+irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and 
> 	+smp_affinity is a bitmask, in which you can specify which CPUs can handle the 
> 	+default_smp_affinity mask applies to all non-active IRQs. In other words IRQs 
> 
>     (Granted, there are already about 300 hundred trailing whitespaces in that file,
>     so this is like trying not to spit into the Pacific ocean ;).
> 
> 2.  I think that the following line should be removed from kernel/irq/proc.c:
> 
> 	+extern cpumask_t irq_default_affinity;
> 
> 	(You already pick up that extern from <linux/irq.h>, as it should be.)
> 
> 3.  The trailing period was missing after the line:
> 
> 	irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
> 
>     Might as well add it, after "prof_cpu_mask", while you're there anyway.
> 
> 4.  In the doc:
> 
>     +  > echo 1 > /proc/irq/5/smp_affinity
>     +
>     +This means that only the first CPU will handle the IRQ, but you can also echo
>     +5 which means that only the first and fourth CPU can handle the IRQ.
> 
>     it might be a good idea to not use "5" for both the example CPU
>     and for the example mask.  It increases the chance of a reader
>     getting confused as to which 5 is which.  Perhaps try a different
>     example CPU, such as:
> 
> 	     echo 1 > /proc/irq/2/smp_affinity
> 
> 5. The original Doc text, before your patch, stated that the
>    "The contents of the prof_cpu_mask file ... by default." 
> 
>    After your patch, this statement that the default contents
>    of the prof_cpu_mask file was ffffffff got lost.
>    
> 6. The grammar of the following got mangled a little:
> 
>     +default_smp_affinity mask applies to all non-active IRQs. In other words IRQs
>     +that have not been allocated/activated yet (for which /proc/irq/[0-9]* directory
>     +does not exist).
> 
>     Perhaps the following is better:
> 
>     +The default_smp_affinity mask applies to all non-active IRQs, which are the
>     +IRQs which have not yet been allocated/activated, and hence which lack a
>     +/proc/irq/[0-9]* directory.
>     
> 7.  The lines of code (with their definition of cpumask_t tmp):
>       +	cpus_and(tmp, new_value, cpu_online_map);
>       +	if (cpus_empty(tmp))
>       +		return -EINVAL;
> 
>     can be better written, I'm pretty sure, as:
>       +	if (!cpus_intersects(new_value, cpu_online_map))
>       +		return -EINVAL;
> 
>     Minimizing cpumask_t's as local stack variables is a good thing,
>     especially on some of the high (thousands) count CPU systems that
>     SGI is developing.

Nice (thorough) review. Thanx. I'll update the patch based on your comments.
#7 was definitely "monkey see, monkey do". I cut and pasted it from existing 
mask update without much thought. Will update both places.

Thanx
Max


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