[PATCH 0/4] rcu: trivial adjust for comments

[PATCH 0/4] rcu: trivial adjust for comments

[Wei Yang]

During code reading, I found there are several mismatch between comments
and code implementation.

Adjust the comment for better understanding.

Wei Yang (4):
  rcu: gp_max is protected by root rcu_node's lock
  rcu: grplo/grphi just records CPU number
  rcu: grpnum just records group number
  rcu: use gp_seq instead of rcu_gp_seq for consistency

 kernel/rcu/tree.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

-- 
2.20.1 (Apple Git-117)

[PATCH 1/4] rcu: gp_max is protected by root rcu_node's lock

[Wei Yang]

gp_max is protected by root rcu_node's lock, let's move the definition
to the place where comments indicate.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
 kernel/rcu/tree.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 43991a40b084..ed9b534ad870 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -301,6 +301,8 @@ struct rcu_state {
 	u8	boost ____cacheline_internodealigned_in_smp;
 						/* Subject to priority boost. */
 	unsigned long gp_seq;			/* Grace-period sequence #. */
+	unsigned long gp_max;			/* Maximum GP duration in */
+						/*  jiffies. */
 	struct task_struct *gp_kthread;		/* Task for grace periods. */
 	struct swait_queue_head gp_wq;		/* Where GP task waits. */
 	short gp_flags;				/* Commands for GP task. */
@@ -346,8 +348,6 @@ struct rcu_state {
 						/*  a reluctant CPU. */
 	unsigned long n_force_qs_gpstart;	/* Snapshot of n_force_qs at */
 						/*  GP start. */
-	unsigned long gp_max;			/* Maximum GP duration in */
-						/*  jiffies. */
 	const char *name;			/* Name of structure. */
 	char abbr;				/* Abbreviated name. */
 
-- 
2.20.1 (Apple Git-117)

[PATCH 2/4] rcu: grplo/grphi just records CPU number

[Wei Yang]

We store lowest and highest CPU number belongs to a rcu_node, which is
not the group number.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
 kernel/rcu/tree.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index ed9b534ad870..ce9ab7371706 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -73,8 +73,8 @@ struct rcu_node {
 	unsigned long ffmask;	/* Fully functional CPUs. */
 	unsigned long grpmask;	/* Mask to apply to parent qsmask. */
 				/*  Only one bit will be set in this mask. */
-	int	grplo;		/* lowest-numbered CPU or group here. */
-	int	grphi;		/* highest-numbered CPU or group here. */
+	int	grplo;		/* lowest-numbered CPU here. */
+	int	grphi;		/* highest-numbered CPU here. */
 	u8	grpnum;		/* CPU/group number for next level up. */
 	u8	level;		/* root is at level 0. */
 	bool	wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
-- 
2.20.1 (Apple Git-117)

[PATCH 3/4] rcu: grpnum just records group number

[Wei Yang]

grpnum in rcu_node means the position in its parent, which is not the
CPU number even in last level.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
 kernel/rcu/tree.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index ce9ab7371706..512829eed545 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -75,7 +75,7 @@ struct rcu_node {
 				/*  Only one bit will be set in this mask. */
 	int	grplo;		/* lowest-numbered CPU here. */
 	int	grphi;		/* highest-numbered CPU here. */
-	u8	grpnum;		/* CPU/group number for next level up. */
+	u8	grpnum;		/* group number for next level up. */
 	u8	level;		/* root is at level 0. */
 	bool	wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
 				/*  exit RCU read-side critical sections */
-- 
2.20.1 (Apple Git-117)

[PATCH 4/4] rcu: use gp_seq instead of rcu_gp_seq for consistency

[Wei Yang]

Commit de30ad512a66 ("rcu: Introduce grace-period sequence numbers")
introduce gp_seq in rcu_state/rcu_node/rcu_data. And this field in last
two structure track the one in first.

While the comment use rcu_gp_seq which is a little misleading for
audience. Let's use the exact name gp_seq for consistency.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
 kernel/rcu/tree.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 512829eed545..3356842bc185 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -41,7 +41,7 @@ struct rcu_node {
 	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
 					/*  some rcu_state fields as well as */
 					/*  following. */
-	unsigned long gp_seq;	/* Track rsp->rcu_gp_seq. */
+	unsigned long gp_seq;	/* Track rsp->gp_seq. */
 	unsigned long gp_seq_needed; /* Track furthest future GP request. */
 	unsigned long completedqs; /* All QSes done for this node. */
 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
@@ -149,7 +149,7 @@ union rcu_noqs {
 /* Per-CPU data for read-copy update. */
 struct rcu_data {
 	/* 1) quiescent-state and grace-period handling : */
-	unsigned long	gp_seq;		/* Track rsp->rcu_gp_seq counter. */
+	unsigned long	gp_seq;		/* Track rsp->gp_seq. */
 	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
 	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
 	bool		core_needs_qs;	/* Core waits for quiesc state. */
-- 
2.20.1 (Apple Git-117)

Re: [PATCH 4/4] rcu: use gp_seq instead of rcu_gp_seq for consistency

[Paul E. McKenney]

On Fri, Jun 12, 2020 at 10:07:55AM +0800, Wei Yang wrote:
> Commit de30ad512a66 ("rcu: Introduce grace-period sequence numbers")
> introduce gp_seq in rcu_state/rcu_node/rcu_data. And this field in last
> two structure track the one in first.
> 
> While the comment use rcu_gp_seq which is a little misleading for
> audience. Let's use the exact name gp_seq for consistency.
> 
> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>

I applied and pushed the others -- good eyes, and thank you!

This one does not apply.  Could you please forward-port it to
the "dev" branch of -rcu?

git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git

							Thanx, Paul

> ---
>  kernel/rcu/tree.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 512829eed545..3356842bc185 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -41,7 +41,7 @@ struct rcu_node {
>  	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
>  					/*  some rcu_state fields as well as */
>  					/*  following. */
> -	unsigned long gp_seq;	/* Track rsp->rcu_gp_seq. */
> +	unsigned long gp_seq;	/* Track rsp->gp_seq. */
>  	unsigned long gp_seq_needed; /* Track furthest future GP request. */
>  	unsigned long completedqs; /* All QSes done for this node. */
>  	unsigned long qsmask;	/* CPUs or groups that need to switch in */
> @@ -149,7 +149,7 @@ union rcu_noqs {
>  /* Per-CPU data for read-copy update. */
>  struct rcu_data {
>  	/* 1) quiescent-state and grace-period handling : */
> -	unsigned long	gp_seq;		/* Track rsp->rcu_gp_seq counter. */
> +	unsigned long	gp_seq;		/* Track rsp->gp_seq. */
>  	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
>  	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
>  	bool		core_needs_qs;	/* Core waits for quiesc state. */
> -- 
> 2.20.1 (Apple Git-117)
> 

Re: [PATCH 4/4] rcu: use gp_seq instead of rcu_gp_seq for consistency

[Wei Yang]

On Fri, Jun 12, 2020 at 07:12:48AM -0700, Paul E. McKenney wrote:
>On Fri, Jun 12, 2020 at 10:07:55AM +0800, Wei Yang wrote:
>> Commit de30ad512a66 ("rcu: Introduce grace-period sequence numbers")
>> introduce gp_seq in rcu_state/rcu_node/rcu_data. And this field in last
>> two structure track the one in first.
>> 
>> While the comment use rcu_gp_seq which is a little misleading for
>> audience. Let's use the exact name gp_seq for consistency.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>
>I applied and pushed the others -- good eyes, and thank you!
>
>This one does not apply.  Could you please forward-port it to
>the "dev" branch of -rcu?
>

The reason is someone has already fixed this :-)

>git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>
>							Thanx, Paul
>
>> ---
>>  kernel/rcu/tree.h | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
>> index 512829eed545..3356842bc185 100644
>> --- a/kernel/rcu/tree.h
>> +++ b/kernel/rcu/tree.h
>> @@ -41,7 +41,7 @@ struct rcu_node {
>>  	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
>>  					/*  some rcu_state fields as well as */
>>  					/*  following. */
>> -	unsigned long gp_seq;	/* Track rsp->rcu_gp_seq. */
>> +	unsigned long gp_seq;	/* Track rsp->gp_seq. */
>>  	unsigned long gp_seq_needed; /* Track furthest future GP request. */
>>  	unsigned long completedqs; /* All QSes done for this node. */
>>  	unsigned long qsmask;	/* CPUs or groups that need to switch in */
>> @@ -149,7 +149,7 @@ union rcu_noqs {
>>  /* Per-CPU data for read-copy update. */
>>  struct rcu_data {
>>  	/* 1) quiescent-state and grace-period handling : */
>> -	unsigned long	gp_seq;		/* Track rsp->rcu_gp_seq counter. */
>> +	unsigned long	gp_seq;		/* Track rsp->gp_seq. */
>>  	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
>>  	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
>>  	bool		core_needs_qs;	/* Core waits for quiesc state. */
>> -- 
>> 2.20.1 (Apple Git-117)
>> 

-- 
Wei Yang
Help you, Help me

Re: [PATCH 4/4] rcu: use gp_seq instead of rcu_gp_seq for consistency

[Paul E. McKenney]

On Fri, Jun 12, 2020 at 10:10:25PM +0000, Wei Yang wrote:
> On Fri, Jun 12, 2020 at 07:12:48AM -0700, Paul E. McKenney wrote:
> >On Fri, Jun 12, 2020 at 10:07:55AM +0800, Wei Yang wrote:
> >> Commit de30ad512a66 ("rcu: Introduce grace-period sequence numbers")
> >> introduce gp_seq in rcu_state/rcu_node/rcu_data. And this field in last
> >> two structure track the one in first.
> >> 
> >> While the comment use rcu_gp_seq which is a little misleading for
> >> audience. Let's use the exact name gp_seq for consistency.
> >> 
> >> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> >
> >I applied and pushed the others -- good eyes, and thank you!
> >
> >This one does not apply.  Could you please forward-port it to
> >the "dev" branch of -rcu?
> 
> The reason is someone has already fixed this :-)

That would explain it!  ;-)

							Thanx, Paul

> >git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> >
> >							Thanx, Paul
> >
> >> ---
> >>  kernel/rcu/tree.h | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >> 
> >> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> >> index 512829eed545..3356842bc185 100644
> >> --- a/kernel/rcu/tree.h
> >> +++ b/kernel/rcu/tree.h
> >> @@ -41,7 +41,7 @@ struct rcu_node {
> >>  	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
> >>  					/*  some rcu_state fields as well as */
> >>  					/*  following. */
> >> -	unsigned long gp_seq;	/* Track rsp->rcu_gp_seq. */
> >> +	unsigned long gp_seq;	/* Track rsp->gp_seq. */
> >>  	unsigned long gp_seq_needed; /* Track furthest future GP request. */
> >>  	unsigned long completedqs; /* All QSes done for this node. */
> >>  	unsigned long qsmask;	/* CPUs or groups that need to switch in */
> >> @@ -149,7 +149,7 @@ union rcu_noqs {
> >>  /* Per-CPU data for read-copy update. */
> >>  struct rcu_data {
> >>  	/* 1) quiescent-state and grace-period handling : */
> >> -	unsigned long	gp_seq;		/* Track rsp->rcu_gp_seq counter. */
> >> +	unsigned long	gp_seq;		/* Track rsp->gp_seq. */
> >>  	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
> >>  	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
> >>  	bool		core_needs_qs;	/* Core waits for quiesc state. */
> >> -- 
> >> 2.20.1 (Apple Git-117)
> >> 
> 
> -- 
> Wei Yang
> Help you, Help me