linux-kernel - Re: [PATCH] iommu/amd - Optimize PPR log handling

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Date:   Wed, 30 May 2018 06:52:04 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Gary R Hook <ghook@....com>
Cc:     Gary R Hook <gary.hook@....com>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd - Optimize PPR log handling

On Tue, May 29, 2018 at 12:28:54PM -0500, Gary R Hook wrote:
> No, no numbers. We're still working out how best to test this, and
> suggestions/strategies are welcome.

Maybe run a simple kernel on the CPU that does a memcpy on a larger
portion of mmapped (but yet unmapped) process address space and measure
the time it takes for the kernel to run. The page-fault path in the
iommu-driver is only a small part of the involved code here, but maybe
you already see a difference. Doing a u-benchmark only for that code is
probably a bit more challenging.

> The change is modeled after the function iommu_poll_events(), which is much
> cleaner. The GA log handling should be changed, as well (there are
> superfluous writes in the loop), but I figured, "one thing at a time". This
> is admittedly a minor optimization, but discussions with Tom Lendacky have
> led us down this path.
> 
> Your feedback is appreciated.

Yeah, the patch looks good to me from my first review. But since I can't
test that code myself I was wondering if you did any tests and can share
something with me to run my own tests :)

	Joerg