linux-kernel - Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations

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Date:   Tue, 16 Jun 2020 11:53:12 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-rdma@...r.kernel.org,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Thomas Hellstrom <thomas.hellstrom@...el.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        linux-media@...r.kernel.org,
        Christian König <christian.koenig@....com>,
        Mika Kuoppala <mika.kuoppala@...el.com>
Subject: Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep
 annotations

On Tue, Jun 16, 2020 at 02:07:19PM +0200, Daniel Vetter wrote:
> > > I've pinged a bunch of armsoc gpu driver people and ask them how much this
> > > hurts, so that we have a clear answer. On x86 I don't think we have much
> > > of a choice on this, with userptr in amd and i915 and hmm work in nouveau
> > > (but nouveau I think doesn't use dma_fence in there). 
> > 
> > Right, nor will RDMA ODP. 
> 
> Hm, what's the context here? I thought RDMA side you really don't want
> dma_fence in mmu_notifiers, so not clear to me what you're agreeing on
> here.

rdma does not use dma_fence at all, and though it is hard to tell, I
didn't notice a dma_fence in the nouveau invalidation call path.

At the very least I think there should be some big warning that
dma_fence in notifiers should be avoided.

Ie it is strange that the new totally-not-a-gpu drivers use dma_fence,
they surely don't have the same constraints as the existing GPU world,
and it would be annoying to see dma_fence notifiers spring up in them

Jason