On Tue, May 09, 2006 at 06:20:12PM +1000, Nick Piggin wrote:
> Balbir Singh wrote:
>
> >On Tue, May 09, 2006 at 03:57:06PM +1000, Nick Piggin wrote:
> >
> >>Well they'll be _collecting_ the stats, yes. Will they really be using
> >>them for anything?
> >>
> >
> >Hmm.. No, the statistics are sent down using the netlink interface
> >to listeners on the netlink group (on every task exit) or to the task that
> >actually requested for the delay accounting data.
> >
> >The stats are currently gathered in kernel and used by user space.
> >
>
> So... what are the consumers of this data going to be? That is my question.
More details on the consumers of this data is available at
http://lkml.org/lkml/2006/3/13/367
>
> >>If you make the whole thing much lighter weight for tasks which aren't
> >>using the accounting, you have a better chance of people turning the
> >>CONFIG option on.
> >>
> >>
> >
> >I am not sure I understand the point completely. Are you suggesting that
> >struct task_delay_info be moved to common data structure as an aggregate
> >containing all the delay stats data?
> >
>
> My suggestion is basically this: if the accounting is going to be used
> infrequently, it might be a good idea to allocate the accounting structures
> on demand, and only perform the accounting when these structures are
> allocated.
>
> It all adds up. Extra cache misses, more icache, more logic, etc... I
> suspect
> that relatively few people will care about these stats.
>
Thanks for clarifying. I now understand your suggestion better.
The accounting is going to be frequent, with data from all tasks in the
system being collected and processed frequently. Since the accounting is
frequent, I think the current scheme works better than on-demand allocation.
Regarding the usefulness of these stats, please see
http://www.uwsg.iu.edu/hypermail/linux/kernel/0604.2/1731.html
Balbir Singh,
Linux Technology Center,
IBM Software Labs
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