From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chuck Ebbert <76306.1226@compuserve.com>
Date: Wed, 01 Feb 2006 00:50:17 +0000
Subject: Re: boot-time slowdown for measure_migration_cost
Message-Id: <200601311952_MC3-1-B742-9F59@compuserve.com>
List-Id: <linux-ia64.vger.kernel.org>
References: <200601271403.27065.bjorn.helgaas@hp.com>
In-Reply-To: <200601271403.27065.bjorn.helgaas@hp.com>
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To: "Luck, Tony" <tony.luck@intel.com>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>, Ingo Molnar <mingo@elte.hu>, linux-ia64 <linux-ia64@vger.kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>, Linus Torvalds <torvalds@osdl.org>, Andrew Morton <akpm@osdl.org>, "Chen, Kenneth W" <kenneth.w.chen@intel.com>

In-Reply-To: <20060130200026.GA5081@agluck-lia64.sc.intel.com>

On Mon, 30 Jan 2006, Tony Luck wrote:

> Might it be wise to see whether the 2% variation that I saw can be
> repeated on some other architecture?  Bjorn's initial post was just
> questioning whether we need to spend this much time during boot to acquire
> this data.  Now we have *one* data point that on an ia64 with four cpus
> with 9MB cache in a single domain that we can speed the calculation by
> a factor of three with only a 2% loss of accuracy.  Can someone else try
> this patch and post the before/after values for migration_cost from dmesg?

Before:

messages.1:Jan 24 01:19:45 d2 kernel: [    6.377117] migration_cost=9352
messages.1:Jan 27 21:07:55 d2 kernel: [    6.384871] migration_cost=9329
messages.1:Jan 28 11:00:32 d2 kernel: [    6.384215] migration_cost=9338
messages.1:Jan 28 12:55:03 d2 kernel: [    6.389189] migration_cost=9364


After:

messages:Jan 31 07:55:07 d2 kernel: [    1.859359] migration_cost=9274


This was on a dual PII Xeon with 2MB L2 cache.  About 3.5x as fast and
only 1% change.

Maybe the default could be to run the quick test with an option to run the
more-accurate one?

--=20
Chuck