Re: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats

Andrew Morton
2006-06-29T20:01:29Z

On Thu, 29 Jun 2006 15:43:41 -0400
Shailabh Nagar <nagar@watson.ibm.com> wrote:

> >Could be so. But we need to understand how significant the impact of this
> >will be in practice.
> >
> >We could find, once this is deployed is real production environments on
> >large machines that the data loss is sufficiently common and sufficiently
> >serious that the feature needs a lot of rework.
> >
> >Now there's always a risk of that sort of thing happening with all
> >features, but it's usually not this evident so early in the development
> >process. We need to get a better understanding of the risk before
> >proceeding too far.
> >
> >
>
> >And there's always a 100% reliable fix for this: throttling. Make the
> >sender of the messages block until the consumer can catch up.
> >
> Is blocking exits an option ?

I think it has to be an option. I'm sure that some peope under some
circumstances will just want to collect all the data, thank you very much.

And I doubt if it'll be a performance problem for them - the amount of CPU
time per exit will be small - if you're exitting at great frequency then the
stats collecion overhead rises proportionately. That is to be expected.

There will be buffering in the channel, so we'd expect to gather thousands
of records per context switch.

> > In some
> >situations, that is what people will want to be able to do. I suspect a
> >good implementation would be to run a collection daemon on each CPU and
> >make the delivery be cpu-local. That's sounding more like relayfs than
> >netlink.
> >
> >
> Yup...the per-cpu, high speed requirements are up relayfs' alley, unless
> Jamal or netlink folks
> are planning something (or can shed light on) how large flows can be
> managed over netlink. I suspect
> this discussion has happened before :-)

yeah.