Re: [PATCH v2 16/19] locking/lockdep: Use function pointer to avoid constant checks

[Bart Van Assche]

On Mon, 2019-03-18 at 16:57 +-0800, Yuyang Du wrote:
+AD4 +-static inline struct list+AF8-head +ACo-get+AF8-forward+AF8-dep(struct lock+AF8-list +ACo lock)
+AD4 +-+AHs
+AD4 +-       return +ACY-lock-+AD4-class-+AD4-locks+AF8-after+ADs
+AD4 +-+AH0
+AD4 +-
+AD4 +-static inline struct list+AF8-head +ACo-get+AF8-backward+AF8-dep(struct lock+AF8-list +ACo lock)
+AD4 +-+AHs
+AD4 +-       return +ACY-lock-+AD4-class-+AD4-locks+AF8-before+ADs
+AD4 +-+AH0
+AD4 +-
+AD4  static int +AF8AXw-bfs(struct lock+AF8-list +ACo-source+AF8-entry,
+AD4                  void +ACo-data,
+AD4                  int (+ACo-match)(struct lock+AF8-list +ACo-entry, void +ACo-data),
+AD4                  struct lock+AF8-list +ACoAKg-target+AF8-entry,
+AD4 -                int forward)
+AD4 +-                struct list+AF8-head +ACo(+ACo-get+AF8-dep)(struct lock+AF8-list +ACo lock))
+AD4  +AHs
+AD4         struct lock+AF8-list +ACo-entry+ADs
+AD4         struct lock+AF8-list +ACo-lock+ADs
+AD4 +AEAAQA -1392,11 +-1402,7 +AEAAQA static int +AF8AXw-bfs(struct lock+AF8-list +ACo-source+AF8-entry,
+AD4                 goto exit+ADs
+AD4         +AH0
+AD4  
+AD4 -       if (forward)
+AD4 -               head +AD0 +ACY-source+AF8-entry-+AD4-class-+AD4-locks+AF8-after+ADs
+AD4 -       else
+AD4 -               head +AD0 +ACY-source+AF8-entry-+AD4-class-+AD4-locks+AF8-before+ADs
+AD4 -
+AD4 +-       head +AD0 get+AF8-dep(source+AF8-entry)+ADs
+AD4         if (list+AF8-empty(head))
+AD4                 goto exit+ADs
+AD4  
+AD4 +AEAAQA -1410,10 +-1416,7 +AEAAQA static int +AF8AXw-bfs(struct lock+AF8-list +ACo-source+AF8-entry,
+AD4                         goto exit+ADs
+AD4                 +AH0
+AD4  
+AD4 -               if (forward)
+AD4 -                       head +AD0 +ACY-lock-+AD4-class-+AD4-locks+AF8-after+ADs
+AD4 -               else
+AD4 -                       head +AD0 +ACY-lock-+AD4-class-+AD4-locks+AF8-before+ADs
+AD4 +-               head +AD0 get+AF8-dep(lock)+ADs
+AD4  
+AD4                 DEBUG+AF8-LOCKS+AF8-WARN+AF8-ON(+ACE-irqs+AF8-disabled())+ADs
+AD4  
+AD4 +AEAAQA -1445,7 +-1448,7 +AEAAQA static inline int +AF8AXw-bfs+AF8-forwards(struct lock+AF8-list +ACo-src+AF8-entry, void +ACo-data,
+AD4                                  int (+ACo-match)(struct lock+AF8-list +ACo-entry, void +ACo-data),
+AD4                                  struct lock+AF8-list +ACoAKg-target+AF8-entry)
+AD4  +AHs
+AD4 -       return +AF8AXw-bfs(src+AF8-entry, data, match, target+AF8-entry, 1)+ADs
+AD4 +-       return +AF8AXw-bfs(src+AF8-entry, data, match, target+AF8-entry, get+AF8-forward+AF8-dep)+ADs
+AD4  
+AD4  +AH0
+AD4  
+AD4 +AEAAQA -1453,7 +-1456,7 +AEAAQA static inline int +AF8AXw-bfs+AF8-backwards(struct lock+AF8-list +ACo-src+AF8-entry, void +ACo-data,
+AD4                                   int (+ACo-match)(struct lock+AF8-list +ACo-entry, void +ACo-data),
+AD4                                   struct lock+AF8-list +ACoAKg-target+AF8-entry)
+AD4  +AHs
+AD4 -       return +AF8AXw-bfs(src+AF8-entry, data, match, target+AF8-entry, 0)+ADs
+AD4 +-       return +AF8AXw-bfs(src+AF8-entry, data, match, target+AF8-entry, get+AF8-backward+AF8-dep)+ADs
+AD4  
+AD4  +AH0

I think this patch makes the code harder to read. Additionally, if the compiler doesn't
do conditional folding, this patch introduces an indirect branch and hence will make the
lockdep code slower.

Bart.