Date: Tue, 9 Nov 2004 01:43:35 +0100
From: Patrick Mau <mau@oscar.ping.de>
To: Andrew Morton <akpm@osdl.org>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: Workaround for wrapping loadaverage
Message-ID: <20041109004335.GA1822@oscar.prima.de>
Reply-To: Patrick Mau <mau@oscar.ping.de>
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On Mon, Nov 08, 2004 at 03:50:51PM -0800, Andrew Morton wrote:
> 
> (PLease don't remove people from Cc:.  Just do reply-to-all).

Hi Andrew,

sorry, I usually remove people from CC if they're subscribed.

> Patrick Mau <mau@oscar.ping.de> wrote:
> >
> > If you would use 236, 252 and 255 the last to load calculations would
> > get optimized into register shifts during calculation. The precision
> > would be bad, but I personally don't mind loosing the fraction.
> 
> What would be the impact on the precision if we were to use 8 bits of
> fraction?

I didn't have time to check again, but I think I ended up with a load of 0.97
using one runnable process because of rounding errors.

> An upper limit of 1024 tasks sounds a bit squeezy.  Even 8192 is a bit
> uncomfortable.  Maybe we should just reimplement the whole thing, perhaps
> in terms of tuples of 32-bit values: 32 bits each side of the binary point?

We re-calculate the load every 5 seconds. I think it would be OK to
use more bits/registers, it's not that frequently called.

It's 1:30 AM and I had a rough working day, maybe I'll prepare a little patch
tomorrow. I think that 8192 _runnable_ processes seems a bit unusual, but we
also account for uninterruptable processes. Maybe there was some swap/IO
storm that triggered the initial overflow, I'll have to check that first.

Best regards,
Patrick
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