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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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