netdev - Re: [PATCH v9 6/6] iommu/dma: Make flush queue sizes and timeout driver configurable

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Date: Mon, 22 May 2023 18:10:01 +0200
From: Joerg Roedel <joro@...tes.org>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: Matthew Rosato <mjrosato@...ux.ibm.com>, Will Deacon <will@...nel.org>,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>,
	Gerd Bayer <gbayer@...ux.ibm.com>,
	Julian Ruess <julianr@...ux.ibm.com>,
	Pierre Morel <pmorel@...ux.ibm.com>,
	Alexandra Winter <wintera@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>,
	David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>, Andy Gross <agross@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Yong Wu <yong.wu@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Orson Zhai <orsonzhai@...il.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Chunyan Zhang <zhang.lyra@...il.com>, Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Krishna Reddy <vdumpa@...dia.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Jonathan Corbet <corbet@....net>, linux-s390@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, asahi@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
	linux-mediatek@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
	linux-tegra@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v9 6/6] iommu/dma: Make flush queue sizes and timeout
 driver configurable

On Mon, May 15, 2023 at 11:15:56AM +0200, Niklas Schnelle wrote:
> In the s390 IOMMU driver a large fixed queue size and timeout is then
> set together with single queue mode bringing its performance on s390
> paged memory guests on par with the previous s390 specific DMA API
> implementation.

Hmm, the right flush-queue size and timeout settings are more a function
of the endpoint device and device driver than of the iommu driver, no? I
think something like this could also help solving the recently reported
scalability problems in the fq-code, if done right.

Regards,

	Joerg