linux-kernel - Re: [RFC v3 5/8] dmabuf: Add gpu cgroup charge transfer function

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Message-ID: <20220321174530.GB9640@blackbody.suse.cz>
Date:   Mon, 21 Mar 2022 18:45:30 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     "T.J. Mercier" <tjmercier@...gle.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <john.stultz@...aro.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>, kaleshsingh@...gle.com,
        Kenny.Ho@....com, dri-devel@...ts.freedesktop.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [RFC v3 5/8] dmabuf: Add gpu cgroup charge transfer function

Hello.

On Wed, Mar 09, 2022 at 04:52:15PM +0000, "T.J. Mercier" <tjmercier@...gle.com> wrote:
> +int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
> +{
> +#ifdef CONFIG_CGROUP_GPU
> +	struct gpucg *current_gpucg;
> +	int ret = 0;
> +
> +	/*
> +	 * Verify that the cgroup of the process requesting the transfer is the
> +	 * same as the one the buffer is currently charged to.
> +	 */
> +	current_gpucg = gpucg_get(current);
> +	mutex_lock(&dmabuf->lock);
> +	if (current_gpucg != dmabuf->gpucg) {
> +		ret = -EPERM;
> +		goto err;
> +	}

Add a shortcut for gpucg == current_gpucg?

> +
> +	ret = gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
> +	if (ret)
> +		goto err;
> +
> +	dmabuf->gpucg = gpucg;
> +
> +	/* uncharge the buffer from the cgroup it's currently charged to. */
> +	gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);

I think gpucg_* API would need to cater for such transfers too since
possibly transitional breach of a limit during the transfer may
unnecessarily fail the operation.

My 0.02€,
Michal