From: Chris Wilson <chris@chris-wilson.co.uk>
To: dri-devel@lists.freedesktop.org
Cc: "Daniel Vetter" <daniel.vetter@ffwll.ch>,
intel-gfx@lists.freedesktop.org,
"Christian König" <christian.koenig@amd.com>
Subject: [PATCH 2/2] dma-buf: Relax the write-seqlock for reallocating the shared fence list
Date: Fri, 12 Jul 2019 09:03:14 +0100 [thread overview]
Message-ID: <20190712080314.21018-2-chris@chris-wilson.co.uk> (raw)
In-Reply-To: <20190712080314.21018-1-chris@chris-wilson.co.uk>
As the set of shared fences is not being changed during reallocation of
the reservation list, we can skip updating the write_seqlock.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Christian König <christian.koenig@amd.com>
---
drivers/dma-buf/reservation.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 80ecc1283d15..c71b85c8c159 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -157,15 +157,15 @@ int reservation_object_reserve_shared(struct reservation_object *obj,
(ksize(new) - offsetof(typeof(*new), shared)) /
sizeof(*new->shared);
- preempt_disable();
- write_seqcount_begin(&obj->seq);
/*
- * RCU_INIT_POINTER can be used here,
- * seqcount provides the necessary barriers
+ * We are not changing the effective set of fences here so can
+ * merely update the pointer to the new array; both existing
+ * readers and new readers will see exactly the same set of
+ * active (unsignaled) shared fences. Individual fences and the
+ * old array are protected by RCU and so will not vanish under
+ * the gaze of the rcu_read_lock() readers.
*/
- RCU_INIT_POINTER(obj->fence, new);
- write_seqcount_end(&obj->seq);
- preempt_enable();
+ rcu_assign_pointer(obj->fence, new);
if (!old)
return 0;
--
2.22.0
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next prev parent reply other threads:[~2019-07-12 8:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-12 8:03 [PATCH 1/2] dma-buf: Expand reservation_list to fill allocation Chris Wilson
2019-07-12 8:03 ` Chris Wilson [this message]
2019-07-16 9:21 ` [PATCH 2/2] dma-buf: Relax the write-seqlock for reallocating the shared fence list Daniel Vetter
2019-07-16 20:05 ` Chris Wilson
2019-07-12 8:33 ` [PATCH 1/2] dma-buf: Expand reservation_list to fill allocation Michel Dänzer
2019-07-12 8:56 ` ✓ Fi.CI.BAT: success for series starting with [1/2] " Patchwork
2019-07-13 15:38 ` ✓ Fi.CI.IGT: " Patchwork
2019-07-14 7:37 ` [PATCH 1/2] " Koenig, Christian
2019-07-15 10:58 ` Chris Wilson
2019-07-15 11:11 ` Chris Wilson
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