Re: [Patch 0/6] delay accounting & taskstats fixes

[Shailabh Nagar <nagar@watson.ibm.com>]

Christoph Hellwig wrote:
> On Tue, Jul 11, 2006 at 12:23:58AM -0400, Shailabh Nagar wrote:
> 
>>Andrew,
>>
>>Chandra, Balbir & I have been putting taskstats and delay accounting
>>patches through some extensive testing on multiple platforms.
>>
>>Following are a set of patches that fix some bugs found as well as
>>some cleanups of the code. Some results showing the cpumask feature 
>>works as expected will follow separately.
> 
> 
> Btw, did you ever explain what this delay accounting code is useful for
> exactly?  

Yes.
Previous postings have explained the rationale,

http://www.uwsg.indiana.edu/hypermail/linux/kernel/0511.1/2275.html
http://www.uwsg.indiana.edu/hypermail/linux/kernel/0512.0/2152.html

lwn.net had a good summary as always,
http://lwn.net/Articles/173209/




> It's an awfull lot of code that doesn't seem to have a huge
> use.  

The delay accounting part of the code is quite small (just a few
lines of timestamping code place in core kernel code) and much of the
remaining size comes from the interface. Since the interface is designed
to be of generic use towards ANY per-task accounting needs, discussions and
code have been fairly involved. We went through a long discussion of
potential exploiters:

(see thread under [Patch 0/8] per-task delay accounting at
http://www.uwsg.indiana.edu/hypermail/linux/kernel/0603.3/index.html

> While we're at it do you have a pointer to the associated userspace code?
> 

Its part of the patches in Documentation/accounting/getdelays.c

and the last-but-one version of it can be viewed at its location in the -mm
tree:
http://www.linux-m32r.org/lxr/http/source/Documentation/accounting/?a=generic

(The just accepted patches updates the documentation especially the parts
relating to cpumasks but the above should also suffice to give a flavor of
what userspace could do).


Thanks,
Shailabh