linux-kernel - Re: [EXTERNAL] Re: [PATCH] sync_file: Return reasonable timestamp when merging signaled fences

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Message-ID: <20190514075537.GA7483@michael-imgtec>
Date:   Tue, 14 May 2019 15:55:37 +0800
From:   Michael Yang <michael.yang@...tec.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>
CC:     <sumit.semwal@...aro.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <gustavo@...ovan.org>,
        <linux-media@...r.kernel.org>, <linaro-mm-sig@...ts.linaro.org>,
        <gregkh@...uxfoundation.org>
Subject: Re: [EXTERNAL] Re: [PATCH] sync_file: Return reasonable timestamp
 when merging signaled fences

On Thu, May 09, 2019 at 12:46:05PM +0100, Chris Wilson wrote:
> Quoting Michael Yang (2019-05-09 05:34:11)
> > If all the sync points were signaled in both fences a and b,
> > there was only one sync point in merged fence which is a_fence[0].
> > The Fence structure in android framework might be confused about
> > timestamp if there were any sync points which were signaled after
> > a_fence[0]. It might be more reasonable to use timestamp of last signaled
> > sync point to represent the merged fence.
> > The issue can be found from EGL extension ANDROID_get_frame_timestamps.
> > Sometimes the return value of EGL_READS_DONE_TIME_ANDROID is head of
> > the return value of EGL_RENDERING_COMPLETE_TIME_ANDROID.
> > That means display/composition had been completed before rendering
> > was completed that is incorrect.
> > 
> > Some discussion can be found at:
> > https://urldefense.proofpoint.com/v2/url?u=https-3A__android-2Dreview.googlesource.com_c_kernel_common_-2B_907009&d=DwIFaQ&c=bq9ppmgvSw3oQFfR871D_w&r=Ngg6vhouPkgwSIbDMU7rDN0ZfT2Qax50xuWkXXqQ3zw&m=N9R9dXGJ3zk0e0gXNM4tsiro7xCOLlWx6c3HAEseSSw&s=6sY2t9i2wvylWH-rPUlvY1MIuWKjCPzT8SeCgpZOIGk&e= 
> > 
> > Signed-off-by: Michael Yang <michael.yang@...tec.com>
> > ---
> > Hi,
> > I didn't get response since I previously sent this a month ago.
> > Could someone have a chance to look at it please?
> > Thanks.
> >  drivers/dma-buf/sync_file.c | 25 +++++++++++++++++++++++--
> >  1 file changed, 23 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> > index 4f6305c..d46bfe1 100644
> > --- a/drivers/dma-buf/sync_file.c
> > +++ b/drivers/dma-buf/sync_file.c
> > @@ -274,8 +274,29 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
> >         for (; i_b < b_num_fences; i_b++)
> >                 add_fence(fences, &i, b_fences[i_b]);
> >  
> > -       if (i == 0)
> > -               fences[i++] = dma_fence_get(a_fences[0]);
> > +       /* If all the sync pts were signaled, then adding the sync_pt who
> > +        * was the last signaled to the fence.
> > +        */
> > +       if (i == 0) {
> > +               struct dma_fence *last_signaled_sync_pt = a_fences[0];
> > +               int iter;
> > +
> > +               for (iter = 1; iter < a_num_fences; iter++) {
> 
> If there is more than one fence, sync_file->fence is a fence_array and
> its timestamp is what you want. If there is one fence, sync_file->fence
> is a pointer to that fence, and naturally has the right timestamp.
> 
> In short, this should be handled by dma_fence_array_create() when given
> a complete set of signaled fences, it too should inherit the signaled
> status with the timestamp being taken from the last fence. It should
> also be careful to inherit the error status.
> -Chris
Thanks Chris for the inputs. For this case, there will be only one fence
in sync_file->fence after doing sync_file_merge(). Regarding to the current
implementation, dma_fence_array_create() is not called as num_fences is equal
to 1. I was wondering do you suggest that we pass a complete set of signaled
fences to sync_file_set_fence() and handle it in dma_fence_array_create().
Thanks.
- Michael