lkml.org 
[lkml]   [2008]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/3] x86: add cpus_scnprintf function v3
On Wed, Apr 09, 2008 at 01:59:39PM -0700, Mike Travis wrote:
> Greg KH wrote:
> > On Wed, Apr 09, 2008 at 07:51:23PM +0200, Bert Wesarg wrote:
> >> On Tue, Apr 8, 2008 at 8:43 PM, Mike Travis <travis@sgi.com> wrote:
> >>> * Cleanup usages of cpumask_scprintf in the following files and add
> >>> another interface to use cpulist_scnprintf where appropriate.
> >> On Mon, Apr 7, 2008 at 8:22 PM, Mike Travis <travis@sgi.com> wrote:
> >>> Part of the change is readability, but also looking towards the future
> >>> of 16k/64k/??? # of cpus, the straight mask approach will overflow the
> >>> PAGE_SIZE buffer provided (though some pathological cases will overflow
> >>> the range method as well.) So we'll need some advancement in the format
> >>> of the printout.
> >> Btw, I think you can now push for a deprecation of the 'old' mask
> >> attributes, with the justification you have given above. The other
> >> possibility is to change sysfs to provide bigger attribute buffers
> >> (CCed Greg for this).
> >
> > Huh?
> >
> > sysfs is "one value per file", if you are getting close to PAGE_SIZE in
> > any sysfs file, then you are doing something very wrong.
> >
> > What sysfs file currently is trying to output data this big?
> >
> > thanks,
> >
> > greg k-h
>
> Hi Greg,
>
> There's none at the moment. The increase is coming from printing the
> cpuset for various attributes, like cpus on a node, etc. Since it uses
> cpumask_scnprintf(), this prints a bit map representing a cpumask_t.
>
> With the increase to 4096 cpus, this string is now 1152 bytes long. The
> next iteration will have 16384 cpus which will need 4608 bytes to fully
> display, overflowing a standard page. I've added alternate interfaces
> that use cpulist_scnprintf() which has the advantage of collapsing the
> bits into ranges. This though can result in a much larger output size
> if, for example only every other bit is set.
>
> Btw, where does one value per file come from?

Documentation/filesystems/sysfs.txt, while a bit outdated, still
contains this rule.

> I see outputs like:
>
> # cat /proc/self/stat
> 4313 (cat) R 4218 4313 4218 34816 4313 4194304 207 0 0 0 0 0 0 0 20 0 1 0 6802916 5672960 131 18446744073709551615 4194304 4212948 140735962676160 18446744073709551615 140499600349840 0 0 0 0 0 0 0 17 3 0 0 0 0 0

That's fine, it's /proc/, not /sys/ :)

thanks,

greg k-h


\
 
 \ /
  Last update: 2008-04-09 23:19    [W:0.061 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site