locking/pvqspinlock: Correct the type of "old" variable in pv_kick_node()

PATCH Applied Uros Bizjak 4 participants 6 messages Jul 21, 2024 – Jul 29, 2024 Locking primitives

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Uros Bizjak

author

2024-07-21 16:46 UTC #0 lore raw

PATCH 1/1 locking/pvqspinlock: Correct the type of "old" variable in pv_kick_node()

"enum vcpu_state" is not compatible with "u8" type for all targets, resulting in:

error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *'

for LoongArch. Correct the type of "old" variable to "u8".

Cc Peter Zijlstra <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Will Deacon <[email protected]>

Cc Waiman Long <[email protected]>

Cc Boqun Feng <[email protected]>

Fixes fea0e1820b51 ("locking/pvqspinlock: Use try_cmpxchg() in qspinlock_paravirt.h")

Reported-by Bibo Mao <[email protected]>

Signed-off-by Uros Bizjak <[email protected]>

Closes https://lore.kernel.org/lkml/[email protected]/ open here

---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

kernel/locking/qspinlock_paravirt.h +1 -1

index f5a36e67b593..ac2e22502741 100644
@@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
 {
 	struct pv_node *pn = (struct pv_node *)node;
-	enum vcpu_state old = vcpu_halted;
+	u8 old = vcpu_halted;
 	/*
 	 * If the vCPU is indeed halted, advance its state to match that of
 	 * pv_wait_node(). If OTOH this fails, the vCPU was running and will

Signature · 1 line

2.42.0

maobibo

Tested-by on v1 1/1

2024-07-22 09:33 UTC #2 lore raw

In reply to Uros Bizjak

Uros,

Sorry for late reply because of weekend time. This modification works well for me.

In later I want to define pv_node::state as int type on LoongArch because there is only int32/int64 cmpxchg is better supported on the system, however that is another issue.

Tested-by Bibo Mao <[email protected]>

Quoted 34 lines · Uros Bizjak

"enum vcpu_state" is not compatible with "u8" type for all targets, resulting in:
error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *'
for LoongArch. Correct the type of "old" variable to "u8".
Cc Peter Zijlstra <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Will Deacon <[email protected]>
Cc Waiman Long <[email protected]>
Cc Boqun Feng <[email protected]>
Fixes fea0e1820b51 ("locking/pvqspinlock: Use try_cmpxchg() in qspinlock_paravirt.h")
Reported-by Bibo Mao <[email protected]>
Signed-off-by Uros Bizjak <[email protected]>
Closes https://lore.kernel.org/lkml/[email protected]/ open here
---
  kernel/locking/qspinlock_paravirt.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
kernel/locking/qspinlock_paravirt.h +1 -1
index f5a36e67b593..ac2e22502741 100644
@@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
  static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
  {
  	struct pv_node *pn = (struct pv_node *)node;
-	enum vcpu_state old = vcpu_halted;
+	u8 old = vcpu_halted;
  	/*
  	 * If the vCPU is indeed halted, advance its state to match that of
  	 * pv_wait_node(). If OTOH this fails, the vCPU was running and will

Waiman Long

reviewer

2024-07-22 15:13 UTC #3 lore raw

Quoted 5 lines · maobibo

Uros,
Sorry for late reply because of weekend time. This modification works well for me.
In later I want to define pv_node::state as int type on LoongArch because there is only int32/int64 cmpxchg is better supported on the system, however that is another issue.

I thought about changing pv_node::state to int, but that requires changing the pv_wait() call to use int too. That doesn't work because pv_wait() is also used to monitor the state of the lock byte of the qspinlock. In essence, we can't use pvqspinlock if 8-bit cmpxchg isn't supported.

Cheers,
Longman

Quoted 40 lines

Tested-by Bibo Mao <[email protected]>
Quoted 35 lines · Uros Bizjak
"enum vcpu_state" is not compatible with "u8" type for all targets, resulting in:
error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *'
for LoongArch. Correct the type of "old" variable to "u8".
Cc Peter Zijlstra <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Will Deacon <[email protected]>
Cc Waiman Long <[email protected]>
Cc Boqun Feng <[email protected]>
Fixes fea0e1820b51 ("locking/pvqspinlock: Use try_cmpxchg() in qspinlock_paravirt.h")
Reported-by Bibo Mao <[email protected]>
Signed-off-by Uros Bizjak <[email protected]>
Closes https://lore.kernel.org/lkml/[email protected]/ open here
---
kernel/locking/qspinlock_paravirt.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
kernel/locking/qspinlock_paravirt.h +1 -1
index f5a36e67b593..ac2e22502741 100644
@@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock 
 *node, struct mcs_spinlock *prev)
   static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
   {
       struct pv_node *pn = (struct pv_node *)node;
-    enum vcpu_state old = vcpu_halted;
+    u8 old = vcpu_halted;
       /*
        * If the vCPU is indeed halted, advance its state to match that of
* pv_wait_node(). If OTOH this fails, the vCPU was running and will

maobibo

2024-07-23 01:14 UTC #4 lore raw

Quoted 9 lines · Waiman Long

Quoted 5 lines · maobibo
Uros,
Sorry for late reply because of weekend time. This modification works well for me.
In later I want to define pv_node::state as int type on LoongArch because there is only int32/int64 cmpxchg is better supported on the system, however that is another issue.
I thought about changing pv_node::state to int, but that requires changing the pv_wait() call to use int too. That doesn't work because pv_wait() is also used to monitor the state of the lock byte of the qspinlock. In essence, we can't use pvqspinlock if 8-bit cmpxchg isn't supported.

Hi Longman,

yes, your are right. pv_wait also monitors the state of the qspinlock lock byte, so the parameter type about pv_wait must be u8.

LoongArch supports byte cmpxchg, only that word cmpxchg has higher efficiency. By the draft kernel compiling test, pvqspinlock can improve performance greatly when pCPU is shared by multiple vCPUs.

And thanks for your remaindering.

Regards
Bibo Mao

Quoted 46 lines

Cheers,
Longman
Quoted 41 lines
Tested-by Bibo Mao <[email protected]>
Quoted 36 lines · Uros Bizjak
"enum vcpu_state" is not compatible with "u8" type for all targets, resulting in:
error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *'
for LoongArch. Correct the type of "old" variable to "u8".
Cc Peter Zijlstra <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Will Deacon <[email protected]>
Cc Waiman Long <[email protected]>
Cc Boqun Feng <[email protected]>
Fixes fea0e1820b51 ("locking/pvqspinlock: Use try_cmpxchg() in qspinlock_paravirt.h")
Reported-by Bibo Mao <[email protected]>
Signed-off-by Uros Bizjak <[email protected]>
Closes https://lore.kernel.org/lkml/[email protected]/ open here
---
kernel/locking/qspinlock_paravirt.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
kernel/locking/qspinlock_paravirt.h +1 -1
index f5a36e67b593..ac2e22502741 100644
@@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock 
 *node, struct mcs_spinlock *prev)
   static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
   {
       struct pv_node *pn = (struct pv_node *)node;
-    enum vcpu_state old = vcpu_halted;
+    u8 old = vcpu_halted;
       /*
        * If the vCPU is indeed halted, advance its state to match that of
* pv_wait_node(). If OTOH this fails, the vCPU was running and will

tip-bot2 for Uros Bizjak

merge bot Applied

2024-07-29 10:24 UTC #5 lore raw

In reply to Uros Bizjak

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     6623b0217d0c9bed80bfa43b778ce1c0eb03b497
Gitweb:        https://git.kernel.org/tip/6623b0217d0c9bed80bfa43b778ce1c0eb03b497
Author:        Uros Bizjak <[email protected]>
AuthorDate:    Sun, 21 Jul 2024 18:45:41 +02:00
Committer:     Peter Zijlstra <[email protected]>
CommitterDate: Mon, 29 Jul 2024 12:16:21 +02:00

locking/pvqspinlock: Correct the type of "old" variable in pv_kick_node()