From: "Christian König" <christian.koenig@amd.com>
To: Rob Clark <robdclark@gmail.com>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
freedreno <freedreno@lists.freedesktop.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Rob Clark <robdclark@chromium.org>,
Sumit Semwal <sumit.semwal@linaro.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 1/3] dma-fence: Add boost fence op
Date: Thu, 20 May 2021 16:11:21 +0200 [thread overview]
Message-ID: <d65acf46-4c3b-4903-6222-0b81915d355d@amd.com> (raw)
In-Reply-To: <CAF6AEGtg_VnxYrj94AfbAfViK1v8U0ZJyfJjS4taVLMF=YVy+w@mail.gmail.com>
Am 20.05.21 um 16:07 schrieb Rob Clark:
> On Wed, May 19, 2021 at 11:47 PM Christian König
> <christian.koenig@amd.com> wrote:
>> Uff, that looks very hardware specific to me.
> Howso? I'm not sure I agree.. and even if it was not useful for some
> hw, it should be useful for enough drivers (and harm no drivers), so I
> still think it is a good idea
>
> The fallback plan is to go the i915 route and stop using atomic
> helpers and do the same thing inside the driver, but that doesn't help
> any of the cases where you have a separate kms and gpu driver.
Yeah, that's certainly not something we want.
>> As far as I can see you can also implement completely inside the backend
>> by starting a timer on enable_signaling, don't you?
> Not really.. I mean, the fact that something waited on a fence could
> be a useful input signal to gpu freq governor, but it is entirely
> insufficient..
>
> If the cpu is spending a lot of time waiting on a fence, cpufreq will
> clock down so you spend less time waiting. And no problem has been
> solved. You absolutely need the concept of a missed deadline, and a
> timer doesn't give you that.
Ok then I probably don't understand the use case here.
What exactly do you try to solve?
Thanks,
Christian.
>
> BR,
> -R
>
>> Christian.
>>
>> Am 19.05.21 um 20:38 schrieb Rob Clark:
>>> From: Rob Clark <robdclark@chromium.org>
>>>
>>> Add a way to hint to the fence signaler that a fence waiter has missed a
>>> deadline waiting on the fence.
>>>
>>> In some cases, missing a vblank can result in lower gpu utilization,
>>> when really we want to go in the opposite direction and boost gpu freq.
>>> The boost callback gives some feedback to the fence signaler that we
>>> are missing deadlines, so it can take this into account in it's freq/
>>> utilization calculations.
>>>
>>> Signed-off-by: Rob Clark <robdclark@chromium.org>
>>> ---
>>> include/linux/dma-fence.h | 26 ++++++++++++++++++++++++++
>>> 1 file changed, 26 insertions(+)
>>>
>>> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
>>> index 9f12efaaa93a..172702521acc 100644
>>> --- a/include/linux/dma-fence.h
>>> +++ b/include/linux/dma-fence.h
>>> @@ -231,6 +231,17 @@ struct dma_fence_ops {
>>> signed long (*wait)(struct dma_fence *fence,
>>> bool intr, signed long timeout);
>>>
>>> + /**
>>> + * @boost:
>>> + *
>>> + * Optional callback, to indicate that a fence waiter missed a deadline.
>>> + * This can serve as a signal that (if possible) whatever signals the
>>> + * fence should boost it's clocks.
>>> + *
>>> + * This can be called in any context that can call dma_fence_wait().
>>> + */
>>> + void (*boost)(struct dma_fence *fence);
>>> +
>>> /**
>>> * @release:
>>> *
>>> @@ -586,6 +597,21 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
>>> return ret < 0 ? ret : 0;
>>> }
>>>
>>> +/**
>>> + * dma_fence_boost - hint from waiter that it missed a deadline
>>> + *
>>> + * @fence: the fence that caused the missed deadline
>>> + *
>>> + * This function gives a hint from a fence waiter that a deadline was
>>> + * missed, so that the fence signaler can factor this in to device
>>> + * power state decisions
>>> + */
>>> +static inline void dma_fence_boost(struct dma_fence *fence)
>>> +{
>>> + if (fence->ops->boost)
>>> + fence->ops->boost(fence);
>>> +}
>>> +
>>> struct dma_fence *dma_fence_get_stub(void);
>>> u64 dma_fence_context_alloc(unsigned num);
>>>
next prev parent reply other threads:[~2021-05-20 14:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 18:38 [RFC 0/3] dma-fence: Add a "boost" mechanism Rob Clark
2021-05-19 18:38 ` [RFC 1/3] dma-fence: Add boost fence op Rob Clark
2021-05-20 6:46 ` Christian König
2021-05-20 14:07 ` Rob Clark
2021-05-20 14:11 ` Christian König [this message]
2021-05-20 14:54 ` Rob Clark
2021-05-20 16:01 ` [Linaro-mm-sig] " Christian König
2021-05-20 16:34 ` Daniel Vetter
2021-05-20 16:40 ` Christian König
2021-05-20 17:08 ` Daniel Vetter
2021-05-21 7:43 ` Christian König
2021-05-21 14:21 ` Daniel Vetter
2021-05-20 16:25 ` Daniel Vetter
2021-05-19 18:38 ` [RFC 2/3] drm/atomic: Call dma_fence_boost() when we've missed a vblank Rob Clark
2021-05-20 16:29 ` Daniel Vetter
2021-05-30 14:33 ` Rob Clark
2021-06-01 14:18 ` Daniel Vetter
2021-06-01 15:46 ` Rob Clark
2021-06-01 16:11 ` Daniel Vetter
2021-05-19 18:38 ` [RFC 3/3] drm/msm: Wire up gpu boost Rob Clark
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