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Date: Tue, 13 Aug 2002 14:24:54 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: "Martin J. Bligh" <Martin.Bligh@us.ibm.com>
cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Andrew Theurer <habanero@us.ibm.com>
Subject: Re: [PATCH] NUMA-Q disable irqbalance
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On Tue, 13 Aug 2002, Martin J. Bligh wrote:
> 
> Was that before or after you changed HZ to 1000? I *think* that increased
> the frequency of IO-APIC reprogramming by a factor of 10, though I might
> be misreading the code. If it does depend on HZ, I think that's bad.

The 1000Hz thing came much later, and I never noticed any impact of that 
on my machines.

(Note that this is all entrely subjective. I was very disappointed in the
feel of the first HT P4 machine I had for the first few weeks, but apart
from running lmbench - which looked ok even though it shows that P4's are
bad at system calls - I've not actually put numbers on it. But my feeling
was that the irq thing made a noticeable difference. Caveat emptor -
subjective feelings are not good).

> People in our benchmarking group (Andrew, cc'ed) have told me that
> reducing the frequency of IO-APIC reprogramming by a factor of 20 or
> so improves performance greatly - don't know what HZ that was at, but
> the whole thing seems a little overenthusiastic to me.

The rebalancing was certainly done with a 100Hz clock, so yes, it might 
have become much worse lately.

		Linus

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