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

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Message-ID: <8b4500da-4ed8-4cd2-ba3b-0c2d0b5b4551@kernel.dk>
Date: Thu, 31 Oct 2024 11:43:50 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>
Cc: 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 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.

-- 
Jens Axboe