From: "Christian König" <christian.koenig@amd.com>
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Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
linux-media@vger.kernel.org, amd-gfx@lists.freedesktop.org,
etnaviv@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
imagination@lists.freedesktop.org, lima@lists.freedesktop.org,
linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org,
nouveau@lists.freedesktop.org, virtualization@lists.linux.dev,
spice-devel@lists.freedesktop.org,
intel-xe@lists.freedesktop.org, linux-tegra@vger.kernel.org,
linux-iio@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [RFC PATCH 0/6] dma-buf: Phase out is_signaled() race
Date: Thu, 29 Oct 2026 14:43:52 +0100 [thread overview]
Message-ID: <2db0f1b4-6628-465e-928e-d779b89f59dc@amd.com> (raw)
In-Reply-To: <3565783722927fa48a30f48b063ef99bcd703eab.camel@mailbox.org>
Hi guys,
On 10/29/26 11:28, Philipp Stanner wrote:
> On Thu, 2026-10-29 at 11:23 +0100, Lucas Stach wrote:
>> Hi Philipp, hi Christian,
>
> Jo Lucas
>
>>
>> Am Donnerstag, dem 29.10.2026 um 10:55 +0100 schrieb Philipp Stanner:
>
> […]
>
>> I think we would all be interested in the actual use-case that's
>> sensitive to this kind of latency.
Well everything which wants things to start as early as possible when the fence is signaled and not wait for the callbacks to run is affected.
If I'm not completely mistaken when we start to wait for the callbacks to finish in is_signaled we break more things than we fix because some people relied on timing here.
> Me too.
>
> Let me use this opportunity to stress that in the future, in DRM,
> whenever we have [to accept] a racy "optimization", both commit
> messages and code comments must document why it exists and who
> requested it with what proof.
That is a really good idea I think.
>
> Would save us lots of time when those things are discussed >5 years
> later.
>
>>
>> However, I wonder if this is even an issue anymore with the lock
>> inlined into the fence structure.
>
> Almost no one uses inline-lock so far. So unfortunately, we might
> regress old drivers, maybe.
Considering that I still get bug reports even for the performance of radeon when we change things I fear that this is true.
Regards,
Christian.
>
> But sounds as if you're in favor of phasing the locklessness out :)
>
>
> P.
prev parent reply other threads:[~2026-10-29 13:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-29 9:55 [RFC PATCH 0/6] dma-buf: Phase out is_signaled() race Philipp Stanner
2026-10-29 9:55 ` [RFC PATCH 1/6] dma-buf: dma-fence: Add flags parameter to dma_fence_init() Philipp Stanner
2026-10-29 13:38 ` Christian König
2026-10-29 9:55 ` [RFC PATCH 2/6] dma-buf: dma-fence: Add flag for using 64-bit seqnos Philipp Stanner
2026-10-29 9:55 ` [RFC PATCH 3/6] dma-buf: Port users of dma_fence_init64() Philipp Stanner
2026-10-29 9:55 ` [RFC PATCH 4/6] dma-buf: dma-fence: remove dma_fence_init64() Philipp Stanner
2026-10-29 9:55 ` [RFC PATCH 5/6] dma-buf: dma-fence: Close race in dma_fence_is_signaled() by default Philipp Stanner
2026-10-29 16:00 ` Matthew Brost
2026-10-29 9:55 ` [RFC PATCH 6/6] drm/nouveau: Remove hacky fence check Philipp Stanner
2026-10-29 10:23 ` [RFC PATCH 0/6] dma-buf: Phase out is_signaled() race Lucas Stach
2026-10-29 10:28 ` Philipp Stanner
2026-10-29 11:23 ` Lucas Stach
2026-10-29 13:43 ` Christian König [this message]
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