Re: taskstats interface for accounting

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

Jay Lan wrote:

> Hi Balbir and Shailabh,
>
> I finally have time to think about implementation details of CSA over
> taskstats interface. I took another look at the taskstats interface
> proposal and was a little bit nervous.
>
> Do you remember i suggested to use #ifdef to cut down traffic and i
> was told a generic netlink header would serve the purpose?
> What i see now at Documentation/accounting/taskstats.txt saying
> NETLINK_GENERIC family is used for unicast query/reply mode. The
> NETLINK_GENERIC family provides great flexsibility on what to receive. 
> However, CSA only uses the multicast mode to receive from kernel
> whenever tasks are existing. I guess i would need to read the netlink
> documentation more carefully to see whether my understanding is
> correct.

I don't think there's a problem here. The netlink socket opened for 
listening to
taskstat data sent on task exit can be done in multicast mode....the 
example code in the
Documentation does that.

>
> Another thing i overlooked when i did the review was that taskstats
> interface is designed to provide _BOTH_ per task _AND_ per thread
> accounting data EVERY TIME a task exists. A thread is an aggregate
> of (per-pid) tasks. Since this type of aggregation is not used in
> CSA, half of data traffic would be useless. Can we add a way to
> configure to not send per-thread data to the socket?

I don't see why not. We could extend the command set to set tgid sending 
on/off.

Regards,
Shailabh

> Regards,
> jay