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Date: Wed, 04 Mar 2026 12:39:08 +0100
Message-Id: <DGTYVZMRVLLE.3HQVL7ZT6MU7H@kernel.org>
Subject: Re: [PATCH v5 2/9] gpu: nova-core: gsp: add mechanism to wait for
 space on command queue
Cc: "Alice Ryhl" <aliceryhl@google.com>, "Alexandre Courbot"
 <acourbot@nvidia.com>, "David Airlie" <airlied@gmail.com>, "Simona Vetter"
 <simona@ffwll.ch>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng"
 <boqun@kernel.org>, "Gary Guo" <gary@garyguo.net>,
 =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, "Benno Lossin"
 <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Trevor
 Gross" <tmgross@umich.edu>, "Zhi Wang" <zhiw@nvidia.com>, "John Hubbard"
 <jhubbard@nvidia.com>, "Alistair Popple" <apopple@nvidia.com>, "Joel
 Fernandes" <joelagnelf@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 <nouveau@lists.freedesktop.org>, <dri-devel@lists.freedesktop.org>,
 <linux-kernel@vger.kernel.org>, <rust-for-linux@vger.kernel.org>
To: "Eliot Courtney" <ecourtney@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260304-cmdq-continuation-v5-0-3f19d759ed93@nvidia.com>
 <20260304-cmdq-continuation-v5-2-3f19d759ed93@nvidia.com>
In-Reply-To: <20260304-cmdq-continuation-v5-2-3f19d759ed93@nvidia.com>

On Wed Mar 4, 2026 at 2:42 AM CET, Eliot Courtney wrote:
> +    fn allocate_command(&mut self, size: usize, timeout: Delta) -> Resul=
t<GspCommand<'_>> {
> +        read_poll_timeout(
> +            || Ok(self.driver_write_area_size()),
> +            |available_bytes| *available_bytes >=3D size_of::<GspMsgElem=
ent>() + size,
> +            Delta::ZERO,

Isn't this either creating unneccessary thrashing of the memory controller =
or
unnecessary contention at the cache-coherency level?

I think we should probably add at least a small delay of something around 1=
us.

> +            timeout,
> +        )?;