linux-kernel - Re: [PATCH v1 00/17] Provide a new two step DMA mapping API

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Message-ID: <20241031204306.GB88858@unreal>
Date: Thu, 31 Oct 2024 22:43:06 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	Keith Busch <kbusch@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
	linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 00/17] Provide a new two step DMA mapping API

On Thu, Oct 31, 2024 at 11:43:50AM -0600, Jens Axboe wrote:
> On 10/31/24 3:37 AM, Leon Romanovsky wrote:
> > On Thu, Oct 31, 2024 at 10:21:13AM +0100, Christoph Hellwig wrote:
> >> On Thu, Oct 31, 2024 at 11:05:30AM +0200, Leon Romanovsky wrote:
> >>> This series is a subset of the series you tested and doesn't include the
> >>> block layer changes which most likely were the cause of the performance
> >>> regression.
> >>>
> >>> This is why I separated the block layer changes from the rest of the series
> >>> and marked them as RFC.
> >>>
> >>> The current patch set is viable for HMM and VFIO. Can you please retest
> >>> only this series and leave the block layer changes for later till Christoph
> >>> finds the answer for the performance regression?
> >>
> >> As the subset doesn't touch block code or code called by block I don't
> >> think we need Jens to benchmark it, unless he really wants to.
> > 
> > He wrote this sentence in his email, while responding on subset which
> > doesn't change anything in block layer: "just want to make sure
> > something like this doesn't get merged until that is both fully
> > understood and sorted out."
> > 
> > This series works like a charm for RDMA (HMM) and VFIO.
> 
> I don't care about rdma/vfio, nor do I test it, so you guys can do
> whatever you want there, as long as it doesn't regress the iommu side.
> The block series is separate, so we'll deal with that when we get there.
> 
> I don't know why you CC'ed linux-block on the series.

Because of the second part, which is marked as RFC and based on this
one. I think that it is better to present whole picture to everyone
interested in the discussion.

Thanks

> 
> -- 
> Jens Axboe
>