From: Segher Boessenkool <segher@kernel.crashing.org>
To: Dave Jones <davej@redhat.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>, mingo@redhat.com
Subject: Re: inaccurate migration cost calculation?
Date: Wed, 3 Jan 2007 19:33:52 +0100 [thread overview]
Message-ID: <f8de460d3c5489f3b1ec407e5d8d8c0b@kernel.crashing.org> (raw)
In-Reply-To: <20070102235733.GG18033@redhat.com>
> Across different boots using the same 2.6.19 kernel on a quad-core xeon
> I see huge variance in the migration_cost being reported during boot.
>
> -migration_cost=39,3940
> +migration_cost=25,4941
>
> This CPU has a very large cache which could be key here...
> L1 Instruction cache: 32KB, 8-way associative. 64 byte line size.
> L1 Data cache: 32KB, 8-way associative. 64 byte line size.
> L3 unified cache: 4MB, 16-way associative. 64 byte line size.
That last cache is shared between CPU cores, which leads
to big non-determinism -- not sure if there's much you can
do about it.
Segher
prev parent reply other threads:[~2007-01-03 18:33 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-02 23:57 inaccurate migration cost calculation? Dave Jones
2007-01-03 18:33 ` Segher Boessenkool [this message]
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