Subject: Re: [patch] scheduler: rebalance_tick interval update
From: Darren Hart <darren@dvhart.com>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: Matt Dobson <colpatch@us.ibm.com>, lkml <linux-kernel@vger.kernel.org>,
       Martin J Bligh <mbligh@aracnet.com>,
       Rick Lindsley <ricklind@us.ibm.com>, Andrew Morton <akpm@osdl.org>,
       Ingo Molnar <mingo@elte.hu>
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Date: Mon, 15 Nov 2004 19:50:04 -0800
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On Tue, 2004-11-16 at 13:27 +1100, Nick Piggin wrote: 
> 
> Nick Piggin wrote:
> 
> >
> > Another example, in some ticks, a CPU won't see the updated 'jiffies', 
> > other
> > times it will (at least on Altix systems, this can happen).
> >
> >
> 
> Note that if you didn't want to have this rash of balancing attempted after
> a CPU wasn't able to run the rebalance for a long time, the solution would
> be to keep adding the balance interval until it becomes greater than the
> current jiffies.

As I mentioned in my last post, I don't think the "synchronized
rebalancing" is a real concern since the interval isn't likely to be the
same and the CPU_OFFSET macro is already in place to prevent this "rash
of balancing" (nice term :-).

> I actually prefer it to try to make up the lost balances, just from the
> perspective of gathering scheduler statistics. 

IMO, scheduler statistics are not worth running load_balance() for no
reason.  (And running it two or three times in a row is clearly not
accomplishing anything)

> I don't suspect it happens
> enough to justify adding the extra logic - Darren, are you actually seeing
> problems?

Not seeing in obvious problems, but the existing logic seems incorrect
to me (and the term last_balanced is currently misleading).  Running
load_balance() multiple times in order to catch up seems wasteful to me
as well.  The current code says something like: run load_balance() 10
times in a second.  If the second is almost up and you have only run it
6 times, it will run it 4 times in a row, that just seems wrong to me.


-- 
Darren Hart <darren@dvhart.com>

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