linux-kernel - Re: [PATCH v3 0/6] ATS capability support for Intel IOMMU

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Message-ID: <20090213034457.GM3624@parisc-linux.org>
Date:	Thu, 12 Feb 2009 20:44:57 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Yu Zhao <yu.zhao@...el.com>
Cc:	jbarnes@...tuousgeek.org, dwmw2@...radead.org,
	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/6] ATS capability support for Intel IOMMU

On Thu, Feb 12, 2009 at 08:50:32PM +0800, Yu Zhao wrote:
>   2, avoid using pci_find_ext_capability every time when reading ATS
>      Invalidate Queue Depth (Matthew Wilcox)

er ... I didn't say it was a problem.  I said I couldn't tell if it was a
problem.  There's no point in taking up an extra 4 bytes per pci_dev if
it's not a performance problem.  How often do we query the queue depth?
Is this something a device driver will call once per device and then
remember for itself, or only use at setup?  Or is it something we call
every millisecond?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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