Messages in this thread | | | Date | Thu, 3 Nov 2005 09:20:14 +0100 (CET) | From | Simon Derr <> | Subject | Re: cpuset - question |
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On Wed, 2 Nov 2005, Paul Jackson wrote:
> Randy asked: > > Just for info, why is this in /dev at all, instead of, say, > > /sys ?? > > Daniel added: > > I'm not sure of the true answer; it is likely that CPUSETS was > > designed in the 2.4 timeframe and compatibility was preferred over the > > clean sysfs interface. > > No .. cpusets was a fresh design for Linux 2.6. The two primary > authors were Simon Derr of Bull and myself of SGI. So far as I > know, Bull did not have Linux 2.4 precedents. SGI had both Linux > 2.4 precedents and Irix precedents. I chose not to propose either > of these SGI precedent API's for the Linux mainline kernel. > > Simon proposed the primary interface for the /dev/cpuset, and I gladly > joined him as his design was superior. Simon had this file system > mounted under /proc, and Christoph Hellwig (our primary reviewer - > thanks!) objected, recommending /dev/cpuset as the mount point instead. > > In Christoph's own words on May 13, 2004: > > - don't mount the filesystem in procfs. the whole point of a new > fs is to move away from the procfs mess! /dev/cpuset/ sounds like > a saner mtpnt. > > In any case, there are two aspects to this question. Should the > cpuset hierarchy be a separate virtual file system of its own, or part > of the sysfs file system? Then, if it is separate, where should it > be mounted. >
There were also a few technical reasons.
The first was the desire to create cpusets with 'mkdir my_cpuset'. But this was not a sufficient reason to have a new filesystem, so after my first version of the cpuset patch I reworked it to use sysfs.
However then I ran into a wall: sysfs does not support files larger than a page. And this was a showstopper as the size of the `tasks' file can be large.
So I had to drop sysfs.
Simon.
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