From: Gary R Hook <ghook@amd.com>
To: Joerg Roedel <joro@8bytes.org>, Gary R Hook <gary.hook@amd.com>
Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/amd - Optimize PPR log handling
Date: Tue, 29 May 2018 12:28:54 -0500 [thread overview]
Message-ID: <223930b9-3df9-813a-6676-68072e4e1bb6@amd.com> (raw)
In-Reply-To: <20180529145405.GN18595@8bytes.org>
On 05/29/2018 09:54 AM, Joerg Roedel wrote:
> Hey Gary,
>
> On Fri, May 18, 2018 at 04:51:56PM -0500, Gary R Hook wrote:
>> Improve the performance of the PPR log polling function (i.e. the
>> task of emptying the log) by minimizing MMIO operations and more
>> efficiently processing groups of log entries. Cache the head
>> pointer, as there's never a reason to read it. Ensure the head
>> pointer register is updated every so often, to inform the IOMMU
>> that space is available in the log.
>>
>> Finally, since a single pass may leave logged events unread, use
>> an outer loop to repeat until head has caught up to tail.
>>
>> Signed-off-by: Gary R Hook <gary.hook@amd.com>
>
> Do you have numbers for the performance improvement? How did you test
> this patch?
No, no numbers. We're still working out how best to test this, and
suggestions/strategies are welcome.
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.
Gary
next prev parent reply other threads:[~2018-05-29 17:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 21:51 [PATCH] iommu/amd - Optimize PPR log handling Gary R Hook
2018-05-29 14:54 ` Joerg Roedel
2018-05-29 17:28 ` Gary R Hook [this message]
2018-05-30 4:52 ` Joerg Roedel
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