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Date: Sun, 12 Dec 2004 23:23:12 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: Pavel Machek <pavel@suse.cz>
Cc: linux-kernel@vger.kernel.org
Subject: Re: dynamic-hz
Message-ID: <20041212222312.GN16322@dualathlon.random>
References: <20041211142317.GF16322@dualathlon.random> <20041212163547.GB6286@elf.ucw.cz>
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On Sun, Dec 12, 2004 at 05:35:47PM +0100, Pavel Machek wrote:
> It certainly helps with singing capacitors... What is overhead of

;)

> this?

The overhead is a single l1 cacheline in the paths manipulating HZ
(rather than having an immediate value hardcoded in the asm, it reads it
from a memory location not in the icache). Plus there are some
conversion routines in the USER_HZ usages. It's not a measurable
difference.