[PATCH 4/4] drm/ttm: Optimize reservation slightly
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Note that thit commit may be obsoleted by the cross-device reservation work.
Signed-off-by: Thomas Hellstrom
---
drivers/gpu/drm/ttm/ttm_bo.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
struct ttm_bo_global *glob = bo->glob;
int ret;
- while (unlikely(atomic_cmpxchg(>reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_read(>reserved) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
return ret;
}
+ atomic_set(>reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,
--
1.7.4.4
[PATCH 4/4] drm/ttm: Optimize reservation slightly
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Note that thit commit may be obsoleted by the cross-device reservation work.
Signed-off-by: Thomas Hellstrom thellst...@vmware.com
---
drivers/gpu/drm/ttm/ttm_bo.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
struct ttm_bo_global *glob = bo-glob;
int ret;
- while (unlikely(atomic_cmpxchg(bo-reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_read(bo-reserved) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
return ret;
}
+ atomic_set(bo-reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,
--
1.7.4.4
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[PATCH 4/4] drm/ttm: Optimize reservation slightly
On 11/05/2012 03:01 PM, Maarten Lankhorst wrote: > Hey, > > Op 05-11-12 14:31, Thomas Hellstrom schreef: >> Reservation locking currently always takes place under the LRU spinlock. >> Hence, strictly there is no need for an atomic_cmpxchg call; we can use >> atomic_read followed by atomic_write since nobody else will ever reserve >> without the lru spinlock held. >> At least on Intel this should remove a locked bus cycle on successful >> reserve. >> >> Signed-off-by: Thomas Hellstrom >> > Is that really a good thing to submit when I am busy killing lru lock around > reserve? :-) > If your patch series makes it into the same kernel, let's kill this patch. Otherwise it may live at least for a kernel release. It's not a big thing to rebase against, and I won't complain if your patch adds another atomic read-modify-write op here. :) /Thomas
[PATCH 4/4] drm/ttm: Optimize reservation slightly
Hey,
Op 05-11-12 14:31, Thomas Hellstrom schreef:
> Reservation locking currently always takes place under the LRU spinlock.
> Hence, strictly there is no need for an atomic_cmpxchg call; we can use
> atomic_read followed by atomic_write since nobody else will ever reserve
> without the lru spinlock held.
> At least on Intel this should remove a locked bus cycle on successful
> reserve.
>
> Signed-off-by: Thomas Hellstrom
>
Is that really a good thing to submit when I am busy killing lru lock around
reserve? :-)
- while (unlikely(atomic_cmpxchg(>reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_xchg(>reserved, 1) != 0)) {
Works without lru lock too!
In fact mutexes are done in a similar way[1], except with some more magic, and
unlocked state is 1, not 0.
However I do think that to get that right (saves a irq disable in unlock path,
and less wakeups in contended
case), I should really just post the mutex extension patches for reservations
and ride the flames. It's
getting too close to real mutexes so I really want it to be a mutex in that
case. So lets convert it.. Soon! :-)
~Maarten
[1] See linux/include/asm-generic/mutex-xchg.h and
linux/include/asm-generic/mutex-dec.h for how
archs generally implement mutex fastpaths.
[PATCH 4/4] drm/ttm: Optimize reservation slightly
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Signed-off-by: Thomas Hellstrom
---
drivers/gpu/drm/ttm/ttm_bo.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
struct ttm_bo_global *glob = bo->glob;
int ret;
- while (unlikely(atomic_cmpxchg(>reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_read(>reserved) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
return ret;
}
+ atomic_set(>reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,
--
1.7.4.4
[PATCH 4/4] drm/ttm: Optimize reservation slightly
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Signed-off-by: Thomas Hellstrom
---
drivers/gpu/drm/ttm/ttm_bo.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
struct ttm_bo_global *glob = bo->glob;
int ret;
- while (unlikely(atomic_cmpxchg(>reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_read(>reserved) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
return ret;
}
+ atomic_set(>reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,
--
1.7.4.4
[PATCH 4/4] drm/ttm: Optimize reservation slightly
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Signed-off-by: Thomas Hellstrom thellst...@vmware.com
---
drivers/gpu/drm/ttm/ttm_bo.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
struct ttm_bo_global *glob = bo-glob;
int ret;
- while (unlikely(atomic_cmpxchg(bo-reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_read(bo-reserved) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
return ret;
}
+ atomic_set(bo-reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,
--
1.7.4.4
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Re: [PATCH 4/4] drm/ttm: Optimize reservation slightly
Hey,
Op 05-11-12 14:31, Thomas Hellstrom schreef:
Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.
Signed-off-by: Thomas Hellstrom thellst...@vmware.com
Is that really a good thing to submit when I am busy killing lru lock around
reserve? :-)
- while (unlikely(atomic_cmpxchg(bo-reserved, 0, 1) != 0)) {
+ while (unlikely(atomic_xchg(bo-reserved, 1) != 0)) {
Works without lru lock too!
In fact mutexes are done in a similar way[1], except with some more magic, and
unlocked state is 1, not 0.
However I do think that to get that right (saves a irq disable in unlock path,
and less wakeups in contended
case), I should really just post the mutex extension patches for reservations
and ride the flames. It's
getting too close to real mutexes so I really want it to be a mutex in that
case. So lets convert it.. Soon! :-)
~Maarten
[1] See linux/include/asm-generic/mutex-xchg.h and
linux/include/asm-generic/mutex-dec.h for how
archs generally implement mutex fastpaths.
___
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Re: [PATCH 4/4] drm/ttm: Optimize reservation slightly
On 11/05/2012 03:01 PM, Maarten Lankhorst wrote: Hey, Op 05-11-12 14:31, Thomas Hellstrom schreef: Reservation locking currently always takes place under the LRU spinlock. Hence, strictly there is no need for an atomic_cmpxchg call; we can use atomic_read followed by atomic_write since nobody else will ever reserve without the lru spinlock held. At least on Intel this should remove a locked bus cycle on successful reserve. Signed-off-by: Thomas Hellstrom thellst...@vmware.com Is that really a good thing to submit when I am busy killing lru lock around reserve? :-) If your patch series makes it into the same kernel, let's kill this patch. Otherwise it may live at least for a kernel release. It's not a big thing to rebase against, and I won't complain if your patch adds another atomic read-modify-write op here. :) /Thomas ___ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
