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    SubjectRe: [PATCH 2/2] x86: modify show_shared_cpu_map in intel_cacheinfo
    Bert Wesarg wrote:
    > 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 did look at that site. Besides being "kind of" out of date (last mod: 10/19/07),
    it didn't appear to track changes in information displayed by proc/sysfs functions.

    >
    > 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?

    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.

    Thanks,
    Mike


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