Hi Maarten, I tested your changes and needed the attached patch: behavior now seems equivalent as android sync. I haven't tested performance.
The issue resolved by this patch happens when i_b < b->num_fences and i_a >= a->num_fences (or vice versa). Then, pt_a is invalid and so dereferencing pt_a->context causes a crash.
On Mon, Nov 4, 2013 at 2:31 AM, Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx> wrote:
op 02-11-13 22:36, Colin Cross schreef:
Well, here I did the same for dma-fence, can you take a look?> On Wed, Oct 30, 2013 at 5:17 AM, Maarten Lankhorst
> <maarten.lankhorst@xxxxxxxxxxxxx> wrote:
>> op 24-10-13 14:13, Maarten Lankhorst schreef:
>>> So I actually tried to implement it now. I killed all the deprecated members and assumed a linear timeline.
>>> This means that syncpoints can only be added at the end, not in between. In particular it means sw_sync
>>> might be slightly broken.
>>>
>>> I only tested it with a simple program I wrote called ufence.c, it's in drivers/staging/android/ufence.c in the following tree:
>>>
>>> http://cgit.freedesktop.org/~mlankhorst/linux
>>>
>>> the "rfc: convert android to fence api" has all the changes from my dma-fence proposal to what android would need,
>>> it also converts the userspace fence api to use the dma-fence api.
>>>
>>> sync_pt is implemented as fence too. This meant not having to convert all of android right away, though I did make some changes.
>>> I killed the deprecated members and made all the fence calls forward to the sync_timeline_ops. dup and compare are no longer used.
>>>
>>> I haven't given this a spin on a full android kernel, only with the components that are in mainline kernel under staging and my dumb test program.
>>>
>>> ~Maarten
>>>
>>> PS: The nomenclature is very confusing. I want to rename dma-fence to syncpoint, but I want some feedback from the android devs first. :)
>>>
>> Come on, any feedback? I want to move the discussion forward.
>>
>> ~Maarten
> I experimented with it a little on a device that uses sync and came
> across a few bugs:
> 1. sync_timeline_signal needs to call __fence_signal on all signaled
> points on the timeline, not just the first
> 2. fence_add_callback doesn't always initialize cb.node
> 3. sync_fence_wait should take ms
> 4. sync_print_pt status printing was incorrect
> 5. there is a deadlock:
> sync_print_obj takes obj->child_list_lock
> sync_print_pt
> fence_is_signaled
> fence_signal takes fence->lock == obj->child_list_lock
> 6. freeing a timeline before all the fences holding points on that
> timeline have timed out results in a crash
>
> With the attached patch to fix these issues, our libsync and sync_test
> give the same results as with our sync code. I haven't tested against
> the full Android framework yet.
>
> The compare op and timeline ordering is critical to the efficiency of
> sync points on Android. The compare op is used when merging fences to
> drop all but the latest point on the same timeline. This is necessary
> for example when the same buffer is submitted to the display on
> multiple frames, like when there is a live wallpaper in the background
> updating at 60 fps and a static screen of widgets on top of it. The
> static widget buffer is submitted on every frame, returning a new
> fence each time. The compositor merges the new fence with the fence
> for the previous buffer, and because they are on the same timeline it
> merges down to a single point. I experimented with disabling the
> merge optimization on a Nexus 10, and found that leaving the screen on
> running a live wallpaper eventually resulted in 100k outstanding sync
> points.
---
diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index 2c7fd3f2ab23..d1d89f1f8553 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -232,39 +232,62 @@ void sync_fence_install(struct sync_fence *fence, int fd)
}
EXPORT_SYMBOL(sync_fence_install);
+static void sync_fence_add_pt(struct sync_fence *fence, int *i, struct fence *pt) {
+ fence->cbs[*i].sync_pt = pt;
+ fence->cbs[*i].fence = fence;
+
+ if (!fence_add_callback(pt, &fence->cbs[*i].cb, fence_check_cb_func)) {
+ fence_get(pt);
+ (*i)++;
+ }
+}
+
struct sync_fence *sync_fence_merge(const char *name,struct sync_fence *a, struct sync_fence *b)
{
int num_fences = a->num_fences + b->num_fences;
struct sync_fence *fence;
- int i;
+ int i, i_a, i_b;
fence = sync_fence_alloc(offsetof(struct sync_fence, cbs[num_fences]), name);
if (fence == NULL)
return NULL;
- fence->num_fences = num_fences;
atomic_set(&fence->status, num_fences);
- for (i = 0; i < a->num_fences; ++i) {
- struct fence *pt = a->cbs[i].sync_pt;
-
- fence_get(pt);
- fence->cbs[i].sync_pt = pt;
- fence->cbs[i].fence = fence;
- if (fence_add_callback(pt, &fence->cbs[i].cb, fence_check_cb_func))- atomic_dec(&fence->status);
+ /*
+ * Assume sync_fence a and b are both ordered and have no
+ * duplicates with the same context.
+ *
+ * If a sync_fence can only be created with sync_fence_merge
+ * and sync_fence_create, this is a reasonable assumption.
+ */
+ for (i = i_a = i_b = 0; i_a < a->num_fences || i_b < b->num_fences; ) {
+ struct fence *pt_a = i_a < a->num_fences ? a->cbs[i_a].sync_pt : NULL;
+ struct fence *pt_b = i_b < b->num_fences ? b->cbs[i_b].sync_pt : NULL;
+
+ if (!pt_b || pt_a->context < pt_b->context) {
+ sync_fence_add_pt(fence, &i, pt_a);
+
+ i_a++;
+ } else if (!pt_a || pt_a->context > pt_b->context) {
+ sync_fence_add_pt(fence, &i, pt_b);
+
+ i_b++;
+ } else {
+ if (pt_a->seqno - pt_b->seqno <= INT_MAX)
+ sync_fence_add_pt(fence, &i, pt_a);
+ else
+ sync_fence_add_pt(fence, &i, pt_b);
+
+ i_a++;
+ i_b++;
+ }
}
- for (i = 0; i < b->num_fences; ++i) {
- struct fence *pt = b->cbs[i].sync_pt;
-
- fence_get(pt);
- fence->cbs[a->num_fences + i].sync_pt = pt;
- fence->cbs[a->num_fences + i].fence = fence;
- if (fence_add_callback(pt, &fence->cbs[a->num_fences + i].cb, fence_check_cb_func))- atomic_dec(&fence->status);
- }
+ if (num_fences > i)
+ atomic_sub(num_fences - i, &fence->status);
+ fence->num_fences = i;
sync_fence_debug_add(fence);
return fence;
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From a440530a29682c595ad69b8cbb35c568228a8777 Mon Sep 17 00:00:00 2001
From: Rom Lemarchand <romlem@xxxxxxxxxx>
Date: Thu, 7 Nov 2013 11:36:08 -0800
Subject: [PATCH] fix
Change-Id: Ie8a10dc466462835456d12962b378158a917a33e
---
drivers/staging/android/sync.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index 1025857..04af0fe 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -266,11 +266,19 @@ struct sync_fence *sync_fence_merge(const char *name,
struct fence *pt_a = a->cbs[i_a].sync_pt;
struct fence *pt_b = b->cbs[i_b].sync_pt;
- if (i_b >= b->num_fences || pt_a->context < pt_b->context) {
+ if (i_b >= b->num_fences) {
sync_fence_add_pt(fence, &i, pt_a);
i_a++;
- } else if (i_a >= a->num_fences || pt_a->context > pt_b->context) {
+ } else if (i_a >= a->num_fences) {
+ sync_fence_add_pt(fence, &i, pt_b);
+
+ i_b++;
+ } else if (pt_a->context < pt_b->context) {
+ sync_fence_add_pt(fence, &i, pt_a);
+
+ i_a++;
+ } else if (pt_a->context > pt_b->context) {
sync_fence_add_pt(fence, &i, pt_b);
i_b++;
--
1.8.4.1
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