linux-kernel - Re: [PATCH 8/8] WIP: add a dma_alloc

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Date:   Tue, 10 Nov 2020 18:50:32 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Ricardo Ribalda <ribalda@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH 8/8] WIP: add a dma_alloc_contiguous API

On Tue, Nov 10, 2020 at 6:33 PM Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> Hi Christoph
>
> On Tue, Nov 10, 2020 at 10:25 AM Christoph Hellwig <hch@....de> wrote:
> >
> > On Mon, Nov 09, 2020 at 03:53:55PM +0100, Ricardo Ribalda wrote:
> > > Hi Christoph
> > >
> > > I have started now to give a try to your patchset. Sorry for the delay.
> > >
> > > For uvc I have prepared this patch:
> > > https://github.com/ribalda/linux/commit/9094fe223fe38f8c8ff21366d893b43cbbdf0113
> > >
> > > I have tested successfully in a x86_64 noteboot..., yes I know there
> > > is no change for that platform :).
> > > I am trying to get hold of an arm device that can run the latest
> > > kernel from upstream.
> > >
> > > On the meanwhile if you could take a look to the patch to verify that
> > > this the way that you expect the drivers to use your api I would
> > > appreciate it
> >
> > This looks pretty reaosnable.
> >
>
> Great
>

Thanks Christoph for taking a look quickly.

> Also FYI, I managed to boot an ARM device with that tree. But I could
> not test the uvc driver (it was a remote device with no usb device
> attached)
>
> Hopefully I will be able to test it for real this week.
>
> Any suggestions for how to measure performance difference?

Back in time Kieran (+CC) shared a patch to add extra statistics for
packet processing and payload assembly, with results of various
approaches summarized in a spreadsheet:
https://docs.google.com/spreadsheets/d/1uPdbdVcebO9OQ0LQ8hR2LGIEySWgSnGwwhzv7LPXAlU/edit#gid=0

That and just simple CPU usage comparison would be enough.

>
> Thanks!
>
> > Note that ifdef  CONFIG_DMA_NONCOHERENT in the old code doesn't actually
> > work, as that option is an internal thing just for mips and sh..

In what terms it doesn't actually work? Last time I checked some
platforms actually defined CONFIG_DMA_NONCOHERENT, so those would
instead use the kmalloc() + dma_map() path. I don't have any
background on why that was added and whether it needs to be preserved,
though. Kieran, Laurent, do you have any insight?

Best regards,
Tomasz