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Subject[PATCH 0/3] x86: add cpuset_scnprintf function

* Add a new cpuset_scnprintf and a sysctl flag to control how cpumask sets
are printed. The default is to use the current cpumask_scnprintf. If
kernel.compat_cpuset_printf is '0' (default 1), then cpulist_scnprintf
is used. In addition, a nodeset_scnprintf is provided for compatibilty.

This is introduced with a CONFIG_KERN_COMPAT_CPUSET_PRINTF flag which
currently is only defined for X86_64_SMP architecture. For all other
architectures the current cpumask_scnprintf() is used.

* Modify usages of cpumask_scnprintf to use the new cpuset_scnprintf where
appropriate. The list of files affected are:

arch/x86/kernel/cpu/intel_cacheinfo.c
drivers/base/node.c
drivers/base/topology.c
drivers/pci/pci-sysfs.c
drivers/pci/probe.c
kernel/irq/proc.c
kernel/profile.c
kernel/sched_stats.h
kernel/sysctl.c
kernel/sysctl_check.c
kernel/trace/trace.c

Note that kernel/sched.c is not in this patchset as it has many other changes,
so the change to use cpuset_scnprintf is in another patchset.

For inclusion in x86/latest.

Based on:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
+ x86/latest .../x86/linux-2.6-x86.git
+ sched-devel/latest .../mingo/linux-2.6-sched-devel.git

Cc: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Mike Travis <travis@sgi.com>
---
The discussion that led up to this...

On Fri, Mar 28, 2008 at 3:40 PM, Mike Travis <travis@sgi.com> wrote:
> >
> > Bert Wesarg wrote:
> > > On Fri, Mar 28, 2008 at 12:16 AM, Mike Travis <travis@sgi.com> wrote:
...
> >> + /*
> > >> + * cpulist_scnprintf() has the advantage of compressing
> > >> + * consecutive cpu numbers into a single range which seems
> > >> + * appropriate for cpus on a leaf. This will change what is
> > >> + * output so scripts that process the output will have to change.
> > > So this breaks user space?
> > >
> > > Bert
> >
> > Potentially, yes. But I suspect with 4096 cpus, user scripts will have
> > to change anyways. Currently it is represented as sets of 32 bit mask
> > outputs with comma separators, so 1152 characters would be output.
But you can declare it as a programming error on user space side. If
you change the format, the brown-paper-bag is yours.


On Mon, Mar 31, 2008 at 6:35 PM, Mike Travis <travis@sgi.com> wrote:
> > Bert Wesarg wrote:
> > > On Fri, Mar 28, 2008 at 7:19 PM, Mike Travis <travis@sgi.com> wrote:
> > >> > Aren't the most cpumaps (like cpu/cpu*/topology/*_siblings or
> > >> > node/node*/cpumap) bitmasks?
> > >>
> > >> I did an informal survey and you are right, the majority of references do use
> > >> cpumask_scnprintf instead of cpulist_scnprintf. Maybe the later function was
> > >> added later?
> > >>
> > >> To me though, it would seem that:
> > >>
> > >> 240-255
> > >>
> > >> is more readable than:
> > >>
> > >> 00000000,00000000,00000000,00000000,00000000,00000000,00000000,0000ffff
> > >>
> > >> And as I mentioned, bitmask_parselist() [libbitmask(3)] does parse the output.
> > > But libbitmask has a bitmask_parsehex() too. (but thanks for the
> > > pointer to this code).
> > >
> > > Anyway, your above example is wrong, the most significant bits comes first:
> > >
> > > ffff0000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
> > >
> > > This makes it not more readable, but I think readability isn't in this
> > > case of that much importance.
> >
> > The original problem was how to avoid allocating a large stack space to display
> > cpu ids. By using cpulist_scnprintf, it accomplishes this without, what I think
> > is too much pain. If it's really that much of a problem, I will rework this patch.
> > But the length of the line with 4096 cpus will be 1152 bytes Is this really
> > better?
I ask myself, why is there a temporary buffer allocation in the first
place? In the end it is copied unbounded into the provided buf
argument. Sure your list is mostly shorter than a hex mask, but you
can also not be sure that it fit into the provided buffer. So you can
also use cpumask_scnprintf directly with the buf argument, and provide
a good known upper bound for the size (ie.
cpumask_scnprintf_len(nr_cpu_ids)).

--


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