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SubjectRe: [PATCH 2/2] x86: modify show_shared_cpu_map in intel_cacheinfo
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:
> >> Used cpulist_scnprintf to print cpus on a leaf instead of requiring
> >> a new "cpumask_scnprintf_len" function to determine the size of
> >> the temporary buffer. cpulist_scnprintf can be used to print directly
> >> to the output buffer, eliminating the need for the temporary buffer.
> >>
> >> Based on:
> >> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
> >> git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-x86.git
> >>
> >> Signed-off-by: Mike Travis <travis@sgi.com>
> >> ---
> >> arch/x86/kernel/cpu/intel_cacheinfo.c | 25 +++++++++++++++++--------
> >> 1 file changed, 17 insertions(+), 8 deletions(-)
> >>
> >> --- linux.trees.git.orig/arch/x86/kernel/cpu/intel_cacheinfo.c
> >> +++ linux.trees.git/arch/x86/kernel/cpu/intel_cacheinfo.c
> >> @@ -593,14 +593,23 @@ static ssize_t show_size(struct _cpuid4_
> >>
> >> static ssize_t show_shared_cpu_map(struct _cpuid4_info *this_leaf, char *buf)
> >> {
> >> - int n = 0;
> >> - int len = cpumask_scnprintf_len(nr_cpu_ids);
> >> - char *mask_str = kmalloc(len, GFP_KERNEL);
> >> -
> >> - if (mask_str) {
> >> - cpumask_scnprintf(mask_str, len, this_leaf->shared_cpu_map);
> >> - n = sprintf(buf, "%s\n", mask_str);
> >> - kfree(mask_str);
> >> + /*
> >> + * 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.

>
> Is there a special notice I should provide to announce this change?
I hope so. At least lwn.net has an API changes site:

http://lwn.net/Articles/2.6-kernel-api/

I also looked into MAINTAINERS, but it seems there is no official API
'maintainer'.

>
> (And this output does conform with other syntax for printing and parsing
> strings of bits.)
Aren't the most cpumaps (like cpu/cpu*/topology/*_siblings or
node/node*/cpumap) bitmasks?

Bert
>
> Thanks,
> Mike
>


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