[PATCH V2] cgroup: Trace event cgroup id fields should be u64

[PATCH V2] cgroup: Trace event cgroup id fields should be u64

[William Kucharski]

Various trace event fields that store cgroup IDs were declared as
ints, but cgroup_id(() returns a u64 and the structures and associated
TP_printk() calls were not updated to reflect this.

Fixes: 743210386c03 ("cgroup: use cgrp->kn->id as the cgroup ID")
Signed-off-by: William Kucharski <william.kucharski@oracle.com>
---
V2: Do not remove spaces from macro arguments

 include/trace/events/cgroup.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
index 7f42a3de59e6..1b68c842ac46 100644
--- a/include/trace/events/cgroup.h
+++ b/include/trace/events/cgroup.h
@@ -59,7 +59,7 @@ DECLARE_EVENT_CLASS(cgroup,
 
 	TP_STRUCT__entry(
 		__field(	int,		root			)
-		__field(	int,		id			)
+		__field(	u64,		id			)
 		__field(	int,		level			)
 		__string(	path,		path			)
 	),
@@ -71,7 +71,7 @@ DECLARE_EVENT_CLASS(cgroup,
 		__assign_str(path, path);
 	),
 
-	TP_printk("root=%d id=%d level=%d path=%s",
+	TP_printk("root=%d id=%llu level=%d path=%s",
 		  __entry->root, __entry->id, __entry->level, __get_str(path))
 );
 
@@ -126,7 +126,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 
 	TP_STRUCT__entry(
 		__field(	int,		dst_root		)
-		__field(	int,		dst_id			)
+		__field(	u64,		dst_id			)
 		__field(	int,		dst_level		)
 		__field(	int,		pid			)
 		__string(	dst_path,	path			)
@@ -142,7 +142,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
 		__assign_str(comm, task->comm);
 	),
 
-	TP_printk("dst_root=%d dst_id=%d dst_level=%d dst_path=%s pid=%d comm=%s",
+	TP_printk("dst_root=%d dst_id=%llu dst_level=%d dst_path=%s pid=%d comm=%s",
 		  __entry->dst_root, __entry->dst_id, __entry->dst_level,
 		  __get_str(dst_path), __entry->pid, __get_str(comm))
 );
@@ -171,7 +171,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
 
 	TP_STRUCT__entry(
 		__field(	int,		root			)
-		__field(	int,		id			)
+		__field(	u64,		id			)
 		__field(	int,		level			)
 		__string(	path,		path			)
 		__field(	int,		val			)
@@ -185,7 +185,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
 		__entry->val = val;
 	),
 
-	TP_printk("root=%d id=%d level=%d path=%s val=%d",
+	TP_printk("root=%d id=%llu level=%d path=%s val=%d",
 		  __entry->root, __entry->id, __entry->level, __get_str(path),
 		  __entry->val)
 );
-- 
2.33.1

Re: [PATCH V2] cgroup: Trace event cgroup id fields should be u64

[Steven Rostedt]

On Wed,  1 Dec 2021 09:07:46 -0700
William Kucharski <william.kucharski@oracle.com> wrote:

> Various trace event fields that store cgroup IDs were declared as
> ints, but cgroup_id(() returns a u64 and the structures and associated
> TP_printk() calls were not updated to reflect this.
> 
> Fixes: 743210386c03 ("cgroup: use cgrp->kn->id as the cgroup ID")
> Signed-off-by: William Kucharski <william.kucharski@oracle.com>
> ---
> V2: Do not remove spaces from macro arguments
> 
>  include/trace/events/cgroup.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
> index 7f42a3de59e6..1b68c842ac46 100644
> --- a/include/trace/events/cgroup.h
> +++ b/include/trace/events/cgroup.h
> @@ -59,7 +59,7 @@ DECLARE_EVENT_CLASS(cgroup,
>  
>  	TP_STRUCT__entry(
>  		__field(	int,		root			)
> -		__field(	int,		id			)
> +		__field(	u64,		id			)
>  		__field(	int,		level			)

It's best to move them around to prevent holes. This is not a packed
structure, and the above will create a structure on the ring buffer that
looks like:

	int		root;
	u64		id;
	int		level;
	short		path_offset;
	short		path_size;

(the string() macro is a 4 byte word where the half is the offset of the
actual string and the other half is the size of the string).

Having a 8 byte word between two 4 byte words, will add a 4 byte padding
after the first 4 byte word (before the 8 byte word), and waste space on
the ring buffer.

Better to move it around to be:

  	TP_STRUCT__entry(
  		__field(	int,		root			)
  		__field(	int,		level			)
		__field(	u64,		id			)

That way the two 4 byte words will be together followed directly by the 8
byte word.

>  		__string(	path,		path			)
>  	),
> @@ -71,7 +71,7 @@ DECLARE_EVENT_CLASS(cgroup,
>  		__assign_str(path, path);
>  	),
>  
> -	TP_printk("root=%d id=%d level=%d path=%s",
> +	TP_printk("root=%d id=%llu level=%d path=%s",
>  		  __entry->root, __entry->id, __entry->level, __get_str(path))
>  );
>  
> @@ -126,7 +126,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>  
>  	TP_STRUCT__entry(
>  		__field(	int,		dst_root		)
> -		__field(	int,		dst_id			)
> +		__field(	u64,		dst_id			)

Same here. Just move dst_level above dst_id.

>  		__field(	int,		dst_level		)
>  		__field(	int,		pid			)
>  		__string(	dst_path,	path			)
> @@ -142,7 +142,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>  		__assign_str(comm, task->comm);
>  	),
>  
> -	TP_printk("dst_root=%d dst_id=%d dst_level=%d dst_path=%s pid=%d comm=%s",
> +	TP_printk("dst_root=%d dst_id=%llu dst_level=%d dst_path=%s pid=%d comm=%s",
>  		  __entry->dst_root, __entry->dst_id, __entry->dst_level,
>  		  __get_str(dst_path), __entry->pid, __get_str(comm))
>  );
> @@ -171,7 +171,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
>  
>  	TP_STRUCT__entry(
>  		__field(	int,		root			)
> -		__field(	int,		id			)
> +		__field(	u64,		id			)

And here.

>  		__field(	int,		level			)
>  		__string(	path,		path			)
>  		__field(	int,		val			)
> @@ -185,7 +185,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
>  		__entry->val = val;
>  	),
>  
> -	TP_printk("root=%d id=%d level=%d path=%s val=%d",
> +	TP_printk("root=%d id=%llu level=%d path=%s val=%d",
>  		  __entry->root, __entry->id, __entry->level, __get_str(path),
>  		  __entry->val)
>  );



-- Steve

Re: [PATCH V2] cgroup: Trace event cgroup id fields should be u64

[William Kucharski]

I had pondered that as a consequence for two of the three uses but wasn't sure
if it was worth reordering things; I can easily do so.

What do you suggest for cgroup_migrate as that will have a hole either way
as it's:

        TP_STRUCT__entry(
                __field(        int,            dst_root                )
                __field(        u64,            dst_id                  )
                __field(        int,            dst_level               )
                __field(        int,            pid                     )
                __string(       dst_path,       path                    )
                __string(       comm,           task->comm              )
        ),

if I put dst_level above dst_id, the int for pid field will leave a hole
anyway because the string pointer for dst_path will want to be 64-bit
aligned.

Thanks in advance.

> On Dec 1, 2021, at 9:14 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> On Wed,  1 Dec 2021 09:07:46 -0700
> William Kucharski <william.kucharski@oracle.com> wrote:
> 
>> Various trace event fields that store cgroup IDs were declared as
>> ints, but cgroup_id(() returns a u64 and the structures and associated
>> TP_printk() calls were not updated to reflect this.
>> 
>> Fixes: 743210386c03 ("cgroup: use cgrp->kn->id as the cgroup ID")
>> Signed-off-by: William Kucharski <william.kucharski@oracle.com>
>> ---
>> V2: Do not remove spaces from macro arguments
>> 
>> include/trace/events/cgroup.h | 12 ++++++------
>> 1 file changed, 6 insertions(+), 6 deletions(-)
>> 
>> diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
>> index 7f42a3de59e6..1b68c842ac46 100644
>> --- a/include/trace/events/cgroup.h
>> +++ b/include/trace/events/cgroup.h
>> @@ -59,7 +59,7 @@ DECLARE_EVENT_CLASS(cgroup,
>> 
>> 	TP_STRUCT__entry(
>> 		__field(	int,		root			)
>> -		__field(	int,		id			)
>> +		__field(	u64,		id			)
>> 		__field(	int,		level			)
> 
> It's best to move them around to prevent holes. This is not a packed
> structure, and the above will create a structure on the ring buffer that
> looks like:
> 
> 	int		root;
> 	u64		id;
> 	int		level;
> 	short		path_offset;
> 	short		path_size;
> 
> (the string() macro is a 4 byte word where the half is the offset of the
> actual string and the other half is the size of the string).
> 
> Having a 8 byte word between two 4 byte words, will add a 4 byte padding
> after the first 4 byte word (before the 8 byte word), and waste space on
> the ring buffer.
> 
> Better to move it around to be:
> 
>  	TP_STRUCT__entry(
>  		__field(	int,		root			)
>  		__field(	int,		level			)
> 		__field(	u64,		id			)
> 
> That way the two 4 byte words will be together followed directly by the 8
> byte word.
> 
>> 		__string(	path,		path			)
>> 	),
>> @@ -71,7 +71,7 @@ DECLARE_EVENT_CLASS(cgroup,
>> 		__assign_str(path, path);
>> 	),
>> 
>> -	TP_printk("root=%d id=%d level=%d path=%s",
>> +	TP_printk("root=%d id=%llu level=%d path=%s",
>> 		  __entry->root, __entry->id, __entry->level, __get_str(path))
>> );
>> 
>> @@ -126,7 +126,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>> 
>> 	TP_STRUCT__entry(
>> 		__field(	int,		dst_root		)
>> -		__field(	int,		dst_id			)
>> +		__field(	u64,		dst_id			)
> 
> Same here. Just move dst_level above dst_id.
> 
>> 		__field(	int,		dst_level		)
>> 		__field(	int,		pid			)
>> 		__string(	dst_path,	path			)
>> @@ -142,7 +142,7 @@ DECLARE_EVENT_CLASS(cgroup_migrate,
>> 		__assign_str(comm, task->comm);
>> 	),
>> 
>> -	TP_printk("dst_root=%d dst_id=%d dst_level=%d dst_path=%s pid=%d comm=%s",
>> +	TP_printk("dst_root=%d dst_id=%llu dst_level=%d dst_path=%s pid=%d comm=%s",
>> 		  __entry->dst_root, __entry->dst_id, __entry->dst_level,
>> 		  __get_str(dst_path), __entry->pid, __get_str(comm))
>> );
>> @@ -171,7 +171,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
>> 
>> 	TP_STRUCT__entry(
>> 		__field(	int,		root			)
>> -		__field(	int,		id			)
>> +		__field(	u64,		id			)
> 
> And here.
> 
>> 		__field(	int,		level			)
>> 		__string(	path,		path			)
>> 		__field(	int,		val			)
>> @@ -185,7 +185,7 @@ DECLARE_EVENT_CLASS(cgroup_event,
>> 		__entry->val = val;
>> 	),
>> 
>> -	TP_printk("root=%d id=%d level=%d path=%s val=%d",
>> +	TP_printk("root=%d id=%llu level=%d path=%s val=%d",
>> 		  __entry->root, __entry->id, __entry->level, __get_str(path),
>> 		  __entry->val)
>> );
> 
> 
> 
> -- Steve

Re: [PATCH V2] cgroup: Trace event cgroup id fields should be u64

[Steven Rostedt]

On Wed, 1 Dec 2021 16:27:54 +0000
William Kucharski <william.kucharski@oracle.com> wrote:

> I had pondered that as a consequence for two of the three uses but wasn't sure
> if it was worth reordering things; I can easily do so.
> 
> What do you suggest for cgroup_migrate as that will have a hole either way
> as it's:
> 
>         TP_STRUCT__entry(
>                 __field(        int,            dst_root                )
>                 __field(        u64,            dst_id                  )
>                 __field(        int,            dst_level               )
>                 __field(        int,            pid                     )
>                 __string(       dst_path,       path                    )
>                 __string(       comm,           task->comm              )
>         ),
> 
> if I put dst_level above dst_id, the int for pid field will leave a hole
> anyway because the string pointer for dst_path will want to be 64-bit
> aligned.
> 
> Thanks in advance.
> 

It's not actually a string pointer, both string() macros are really 4 byte
words. The above would be best compressed as:

         TP_STRUCT__entry(
                 __field(        int,            dst_root                )
                 __field(        int,            dst_level               )
                 __field(        u64,            dst_id                  )
                 __field(        int,            pid                     )
                 __string(       dst_path,       path                    )
                 __string(       comm,           task->comm              )
         ),

What that would turn into is:

	struct __entry {
		int		dst_root;
		int		dst_level;
		u64		dst_id;
		int		pid;
		int		dst_path_offset_size;
		int		comm_offset_size;
		char		strings[];
	}

Remember, this is used for storing data onto the ring buffer. I'll make up
two strings to show an example.

  dst_path = "/path/to/dst_path";
  comm = "bash";

The string(dst_path) and string(comm) would be where the data to find the
strings are. The strings will be stored in the strings[] field of the
structure, and the dst_path and comm fields will be used to find those
strings.

	dst_root = 1;
	dst_level = 2;
	dst_id = 3;
	pid = 4;

	dst_path = (28 << 16) | 18;
	comm = ((28 + 18) << 16 | 5;

	strings = "/path/to/dst_path\0bash\0";


The dst_path holds how to find the string it represents. It starts at
offset 28[*] (sizeof(int) * 5 + sizeof(u64))
And has size of 18 (strlen("/path/to/dst_path") + 1)

The comm string starts at offset 46 (28 + size of dst_path), and has he
size of 5 (strlen("bash") + 1).

So consider "string()" macros to be only 4 bytes in size. And leave the
"holes" at the end, especially if there's strings, because the will start
the actual strings nicely aligned.

-- Steve

[*] It really starts at a later offset, because there's common fields added
before the first field (common_type, common_flags, common_preempt_count,
common_pid) that is also included in that offset count.