Re: [PATCH v4 2/2] ksm: provide support to use deferrable timers for scanner thread

[Chintan Pandya]

I don't mean to divert the thread too much. But just one suggestion 
offered by Harshad.

Why can't we stop invoking more of a KSM scanner thread when we are 
saturating from savings ? But again, to check whether savings are 
saturated or not, we may still want to rely upon timers and we have to 
wake the CPUs up from IDLE state.

> > here. Can't we create a new (timer) infrastructure that does the right
> > thing? Surely this isn't the only such case.
>
> A sleep-walking timer, that goes to sleep in one bed, but may wake in
> another; and defers while beds are empty?  I'd be happy to try using
> that for KSM if it already existed, and no doubt Chintan would too

This is interesting for sure :)

> But I don't think KSM presents a very good case for developing it.
> I think KSM's use of a sleep_millisecs timer is really just an apology
> for the amount of often wasted work that it does, and dates from before
> we niced it down 5.  I prefer the idea of a KSM which waits on activity
> amongst the restricted set of tasks it is tracking: as this patch tries.
>
> But my preference may be naive: doing lots of unnecessary work doesn't
> matter as much as waking cpus from deep sleep.

This is exactly the preference we are looking for. But yes, cannot be 
generalized for all.

> > I know both RCU and some NOHZ_FULL muck already track when the system is
> > completely idle. This is yet another case of that.
>
> Hugh


--
Chintan Pandya

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/