Re: [PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
On Tue, Aug 20, 2013 at 05:48:01PM +0800, Lai Jiangshan wrote:
> On 08/20/2013 10:42 AM, Paul E. McKenney wrote:
> > From: "Paul E. McKenney"
> >
> > This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work
> > is done" check in _rcu_barrier(). This applies feedback from Linus
> > (https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
> > in an unrelated patch.
> >
> > Signed-off-by: Paul E. McKenney
> > Reviewed-by: Josh Triplett
> > ---
> > kernel/rcutree.c | 15 +--
> > 1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index c6a064a..612aff1 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
> > * transition. The "if" expression below therefore rounds the old
> > * value up to the next even number and adds two before comparing.
> > */
> > - snap_done = ACCESS_ONCE(rsp->n_barrier_done);
> > + snap_done = rsp->n_barrier_done;
> > _rcu_barrier_trace(rsp, "Check", -1, snap_done);
> > - if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
> > +
> > + /*
> > +* If the value in snap is odd, we needed to wait for the current
> > +* rcu_barrier() to complete, then wait for the next one, in other
> > +* words, we need the value of snap_done to be three larger than
> > +* the value of snap. On the other hand, if the value in snap is
> > +* even, we only had to wait for the next rcu_barrier() to complete,
> > +* in other words, we need the value of snap_done to be only two
> > +* greater than the value of snap. The "(snap + 3) & 0x1" computes
>
> "(snap + 3) & 0x1"
> ==> "(snap + 3) & ~0x1"
Good catch, fixed!
Thanx, Paul
> > +* this for us (thank you, Linus!).
> > +*/
> > + if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
> > _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
> > smp_mb(); /* caller's subsequent code after above check. */
> > mutex_unlock(>barrier_mutex);
>
--
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Re: [PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
On 08/20/2013 10:42 AM, Paul E. McKenney wrote:
> From: "Paul E. McKenney"
>
> This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work
> is done" check in _rcu_barrier(). This applies feedback from Linus
> (https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
> in an unrelated patch.
>
> Signed-off-by: Paul E. McKenney
> Reviewed-by: Josh Triplett
> ---
> kernel/rcutree.c | 15 +--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index c6a064a..612aff1 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
>* transition. The "if" expression below therefore rounds the old
>* value up to the next even number and adds two before comparing.
>*/
> - snap_done = ACCESS_ONCE(rsp->n_barrier_done);
> + snap_done = rsp->n_barrier_done;
> _rcu_barrier_trace(rsp, "Check", -1, snap_done);
> - if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
> +
> + /*
> + * If the value in snap is odd, we needed to wait for the current
> + * rcu_barrier() to complete, then wait for the next one, in other
> + * words, we need the value of snap_done to be three larger than
> + * the value of snap. On the other hand, if the value in snap is
> + * even, we only had to wait for the next rcu_barrier() to complete,
> + * in other words, we need the value of snap_done to be only two
> + * greater than the value of snap. The "(snap + 3) & 0x1" computes
"(snap + 3) & 0x1"
==> "(snap + 3) & ~0x1"
> + * this for us (thank you, Linus!).
> + */
> + if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
> _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
> smp_mb(); /* caller's subsequent code after above check. */
> mutex_unlock(>barrier_mutex);
--
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Re: [PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
On 08/20/2013 10:42 AM, Paul E. McKenney wrote:
From: Paul E. McKenney paul...@linux.vnet.ibm.com
This commit drops an unneeded ACCESS_ONCE() and simplifies an our work
is done check in _rcu_barrier(). This applies feedback from Linus
(https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
in an unrelated patch.
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
Reviewed-by: Josh Triplett j...@joshtriplett.org
---
kernel/rcutree.c | 15 +--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c6a064a..612aff1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
* transition. The if expression below therefore rounds the old
* value up to the next even number and adds two before comparing.
*/
- snap_done = ACCESS_ONCE(rsp-n_barrier_done);
+ snap_done = rsp-n_barrier_done;
_rcu_barrier_trace(rsp, Check, -1, snap_done);
- if (ULONG_CMP_GE(snap_done, ((snap + 1) ~0x1) + 2)) {
+
+ /*
+ * If the value in snap is odd, we needed to wait for the current
+ * rcu_barrier() to complete, then wait for the next one, in other
+ * words, we need the value of snap_done to be three larger than
+ * the value of snap. On the other hand, if the value in snap is
+ * even, we only had to wait for the next rcu_barrier() to complete,
+ * in other words, we need the value of snap_done to be only two
+ * greater than the value of snap. The (snap + 3) 0x1 computes
(snap + 3) 0x1
== (snap + 3) ~0x1
+ * this for us (thank you, Linus!).
+ */
+ if (ULONG_CMP_GE(snap_done, (snap + 3) ~0x1)) {
_rcu_barrier_trace(rsp, EarlyExit, -1, snap_done);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(rsp-barrier_mutex);
--
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Re: [PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
On Tue, Aug 20, 2013 at 05:48:01PM +0800, Lai Jiangshan wrote:
On 08/20/2013 10:42 AM, Paul E. McKenney wrote:
From: Paul E. McKenney paul...@linux.vnet.ibm.com
This commit drops an unneeded ACCESS_ONCE() and simplifies an our work
is done check in _rcu_barrier(). This applies feedback from Linus
(https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
in an unrelated patch.
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
Reviewed-by: Josh Triplett j...@joshtriplett.org
---
kernel/rcutree.c | 15 +--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c6a064a..612aff1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
* transition. The if expression below therefore rounds the old
* value up to the next even number and adds two before comparing.
*/
- snap_done = ACCESS_ONCE(rsp-n_barrier_done);
+ snap_done = rsp-n_barrier_done;
_rcu_barrier_trace(rsp, Check, -1, snap_done);
- if (ULONG_CMP_GE(snap_done, ((snap + 1) ~0x1) + 2)) {
+
+ /*
+* If the value in snap is odd, we needed to wait for the current
+* rcu_barrier() to complete, then wait for the next one, in other
+* words, we need the value of snap_done to be three larger than
+* the value of snap. On the other hand, if the value in snap is
+* even, we only had to wait for the next rcu_barrier() to complete,
+* in other words, we need the value of snap_done to be only two
+* greater than the value of snap. The (snap + 3) 0x1 computes
(snap + 3) 0x1
== (snap + 3) ~0x1
Good catch, fixed!
Thanx, Paul
+* this for us (thank you, Linus!).
+*/
+ if (ULONG_CMP_GE(snap_done, (snap + 3) ~0x1)) {
_rcu_barrier_trace(rsp, EarlyExit, -1, snap_done);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(rsp-barrier_mutex);
--
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the body of a message to majord...@vger.kernel.org
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Please read the FAQ at http://www.tux.org/lkml/
[PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
From: "Paul E. McKenney"
This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work
is done" check in _rcu_barrier(). This applies feedback from Linus
(https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
in an unrelated patch.
Signed-off-by: Paul E. McKenney
Reviewed-by: Josh Triplett
---
kernel/rcutree.c | 15 +--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c6a064a..612aff1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
* transition. The "if" expression below therefore rounds the old
* value up to the next even number and adds two before comparing.
*/
- snap_done = ACCESS_ONCE(rsp->n_barrier_done);
+ snap_done = rsp->n_barrier_done;
_rcu_barrier_trace(rsp, "Check", -1, snap_done);
- if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
+
+ /*
+* If the value in snap is odd, we needed to wait for the current
+* rcu_barrier() to complete, then wait for the next one, in other
+* words, we need the value of snap_done to be three larger than
+* the value of snap. On the other hand, if the value in snap is
+* even, we only had to wait for the next rcu_barrier() to complete,
+* in other words, we need the value of snap_done to be only two
+* greater than the value of snap. The "(snap + 3) & 0x1" computes
+* this for us (thank you, Linus!).
+*/
+ if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
_rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(>barrier_mutex);
--
1.8.1.5
--
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[PATCH tip/core/rcu 8/9] rcu: Simplify _rcu_barrier() processing
From: Paul E. McKenney paul...@linux.vnet.ibm.com
This commit drops an unneeded ACCESS_ONCE() and simplifies an our work
is done check in _rcu_barrier(). This applies feedback from Linus
(https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
in an unrelated patch.
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
Reviewed-by: Josh Triplett j...@joshtriplett.org
---
kernel/rcutree.c | 15 +--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c6a064a..612aff1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp)
* transition. The if expression below therefore rounds the old
* value up to the next even number and adds two before comparing.
*/
- snap_done = ACCESS_ONCE(rsp-n_barrier_done);
+ snap_done = rsp-n_barrier_done;
_rcu_barrier_trace(rsp, Check, -1, snap_done);
- if (ULONG_CMP_GE(snap_done, ((snap + 1) ~0x1) + 2)) {
+
+ /*
+* If the value in snap is odd, we needed to wait for the current
+* rcu_barrier() to complete, then wait for the next one, in other
+* words, we need the value of snap_done to be three larger than
+* the value of snap. On the other hand, if the value in snap is
+* even, we only had to wait for the next rcu_barrier() to complete,
+* in other words, we need the value of snap_done to be only two
+* greater than the value of snap. The (snap + 3) 0x1 computes
+* this for us (thank you, Linus!).
+*/
+ if (ULONG_CMP_GE(snap_done, (snap + 3) ~0x1)) {
_rcu_barrier_trace(rsp, EarlyExit, -1, snap_done);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(rsp-barrier_mutex);
--
1.8.1.5
--
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the body of a message to majord...@vger.kernel.org
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