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Date: Fri, 28 Mar 2008 11:19:37 -0700
From: Mike Travis <travis@....com>
To: Bert Wesarg <bert.wesarg@...glemail.com>
CC: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [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@....com> wrote:
>> Bert Wesarg wrote:
>> > On Fri, Mar 28, 2008 at 12:16 AM, Mike Travis <travis@....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@....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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