| Message ID | 20190811184613.20463-2-urezki@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | some cleanups related to RB_DECLARE_CALLBACKS_MAX | expand |
On Sun, Aug 11, 2019 at 11:46 AM Uladzislau Rezki (Sony) <urezki@gmail.com> wrote: > > Recently there was introduced RB_DECLARE_CALLBACKS_MAX template. > One of the callback, to be more specific *_compute_max(), calculates > a maximum scalar value of node against its left/right sub-tree. > > To simplify the code and improve readability we can switch and > make use of max3() macro that makes the code more transparent. > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Thanks. The change is correct but I think I prefer it the "before" version. My reasons are: - I don't have a strong style preference either way - it's the same amount of code either way, admittedly more modular in your proposal, but also with more indirection (compute_max refers to get_max and max3). The indirection doesn't hinder readability but IMO it makes it harder to be confident that the compiler will generate quality code, compared to the "before" approach which just lays down all the pieces in a linear way. - A quick check shows that the proposed change generates larger code for mm/interval_tree.o: 2757 0 0 2757 ac5 mm/interval_tree.o 2533 0 0 2533 9e5 mm/interval_tree.o.orig This does not happen for every RB_DECLARE_CALLBACKS_MAX use, lib/interval_tree.o in particular seems to be fine. But it does go towards my gut feeling that the change trusts the compiler/optimizer more than I want to. - Slight loss of generality. The "before" code only assumes that the RBAUGMENTED field can be compared using "<" ; the "after" code also assumes that the minimum value is 0. While this covers the current uses, I would prefer not to have that limitation.
> On Sun, Aug 11, 2019 at 11:46 AM Uladzislau Rezki (Sony) > <urezki@gmail.com> wrote: > > > > Recently there was introduced RB_DECLARE_CALLBACKS_MAX template. > > One of the callback, to be more specific *_compute_max(), calculates > > a maximum scalar value of node against its left/right sub-tree. > > > > To simplify the code and improve readability we can switch and > > make use of max3() macro that makes the code more transparent. > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> > > Thanks. The change is correct but I think I prefer it the "before" > version. My reasons are: > > - I don't have a strong style preference either way - it's the same > amount of code either way, admittedly more modular in your proposal, > but also with more indirection (compute_max refers to get_max and > max3). The indirection doesn't hinder readability but IMO it makes it > harder to be confident that the compiler will generate quality code, > compared to the "before" approach which just lays down all the pieces > in a linear way. Thank you for your comments. As for compiler and what can be generated as a result depends on arch, etc, so i agree here. "inline" is a hint only. But it can be rewritten. One way is to use __always_inline another one is: <snip> RBTYPE max = max3(RBCOMPUTE(node), \ node->RBFIELD.rb_left ? \ rb_entry(node->RBFIELD.rb_left, \ RBSTRUCT, RBFIELD)->RBAUGMENTED:0, \ node->RBFIELD.rb_right ? \ rb_entry(node->RBFIELD.rb_right, \ RBSTRUCT, RBFIELD)->RBAUGMENTED:0); <snip> i.e. directly embed an access to the left/right nodes into max3(). That way we can get rid of extra "child" variable and to have a liner code as "before" variant. Again, i am not interested in just pushing this change, the aim was to make it more readable for others and that is it. > > - A quick check shows that the proposed change generates larger code > for mm/interval_tree.o: > 2757 0 0 2757 ac5 mm/interval_tree.o > 2533 0 0 2533 9e5 mm/interval_tree.o.orig > This does not happen for every RB_DECLARE_CALLBACKS_MAX use, > lib/interval_tree.o in particular seems to be fine. But it does go > towards my gut feeling that the change trusts the compiler/optimizer > more than I want to. > I see your point. Indeed the generated code is bit bigger with the change, however with above modification it improves the situation and becomes: <snip> 284544 Aug 13 09:53 interval_tree.o 283192 Aug 13 09:57 interval_tree.o.orig <snip> but is still a bit higher. If we care about that, then i will drop this patch, because "before" code is better in that context. > - Slight loss of generality. The "before" code only assumes that the > RBAUGMENTED field can be compared using "<" ; the "after" code also > assumes that the minimum value is 0. While this covers the current > uses, I would prefer not to have that limitation. If we care about negative augmented values, then we should stick to "before" code. Agree here. If you have any ideas how to extend and cover negative cases, please let me know. Otherwise we can drop this change and do not pay much attention at it. Thank you. -- Vlad Rezki
diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h index fdd421b8d9ae..fb29d6627646 100644 --- a/include/linux/rbtree_augmented.h +++ b/include/linux/rbtree_augmented.h @@ -119,26 +119,26 @@ RBSTATIC const struct rb_augment_callbacks RBNAME = { \ #define RB_DECLARE_CALLBACKS_MAX(RBSTATIC, RBNAME, RBSTRUCT, RBFIELD, \ RBTYPE, RBAUGMENTED, RBCOMPUTE) \ -static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit) \ -{ \ - RBSTRUCT *child; \ - RBTYPE max = RBCOMPUTE(node); \ - if (node->RBFIELD.rb_left) { \ - child = rb_entry(node->RBFIELD.rb_left, RBSTRUCT, RBFIELD); \ - if (child->RBAUGMENTED > max) \ - max = child->RBAUGMENTED; \ - } \ - if (node->RBFIELD.rb_right) { \ - child = rb_entry(node->RBFIELD.rb_right, RBSTRUCT, RBFIELD); \ - if (child->RBAUGMENTED > max) \ - max = child->RBAUGMENTED; \ - } \ - if (exit && node->RBAUGMENTED == max) \ - return true; \ - node->RBAUGMENTED = max; \ - return false; \ -} \ -RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME, \ +static inline RBTYPE RBNAME ## _get_max(struct rb_node *node) \ +{ \ + RBSTRUCT *tmp; \ + \ + tmp = rb_entry_safe(node, RBSTRUCT, RBFIELD); \ + return tmp ? tmp->RBAUGMENTED : 0; \ +} \ + \ +static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit) \ +{ \ + RBTYPE max = max3(RBCOMPUTE(node), \ + RBNAME ## _get_max(node->RBFIELD.rb_left), \ + RBNAME ## _get_max(node->RBFIELD.rb_right)); \ + \ + if (exit && node->RBAUGMENTED == max) \ + return true; \ + node->RBAUGMENTED = max; \ + return false; \ +} \ +RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME, \ RBSTRUCT, RBFIELD, RBAUGMENTED, RBNAME ## _compute_max) diff --git a/tools/include/linux/rbtree_augmented.h b/tools/include/linux/rbtree_augmented.h index 381aa948610d..3b8284479e98 100644 --- a/tools/include/linux/rbtree_augmented.h +++ b/tools/include/linux/rbtree_augmented.h @@ -121,26 +121,26 @@ RBSTATIC const struct rb_augment_callbacks RBNAME = { \ #define RB_DECLARE_CALLBACKS_MAX(RBSTATIC, RBNAME, RBSTRUCT, RBFIELD, \ RBTYPE, RBAUGMENTED, RBCOMPUTE) \ -static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit) \ -{ \ - RBSTRUCT *child; \ - RBTYPE max = RBCOMPUTE(node); \ - if (node->RBFIELD.rb_left) { \ - child = rb_entry(node->RBFIELD.rb_left, RBSTRUCT, RBFIELD); \ - if (child->RBAUGMENTED > max) \ - max = child->RBAUGMENTED; \ - } \ - if (node->RBFIELD.rb_right) { \ - child = rb_entry(node->RBFIELD.rb_right, RBSTRUCT, RBFIELD); \ - if (child->RBAUGMENTED > max) \ - max = child->RBAUGMENTED; \ - } \ - if (exit && node->RBAUGMENTED == max) \ - return true; \ - node->RBAUGMENTED = max; \ - return false; \ -} \ -RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME, \ +static inline RBTYPE RBNAME ## _get_max(struct rb_node *node) \ +{ \ + RBSTRUCT *tmp; \ + \ + tmp = rb_entry_safe(node, RBSTRUCT, RBFIELD); \ + return tmp ? tmp->RBAUGMENTED : 0; \ +} \ + \ +static inline bool RBNAME ## _compute_max(RBSTRUCT *node, bool exit) \ +{ \ + RBTYPE max = max3(RBCOMPUTE(node), \ + RBNAME ## _get_max(node->RBFIELD.rb_left), \ + RBNAME ## _get_max(node->RBFIELD.rb_right)); \ + \ + if (exit && node->RBAUGMENTED == max) \ + return true; \ + node->RBAUGMENTED = max; \ + return false; \ +} \ +RB_DECLARE_CALLBACKS(RBSTATIC, RBNAME, \ RBSTRUCT, RBFIELD, RBAUGMENTED, RBNAME ## _compute_max)
Recently there was introduced RB_DECLARE_CALLBACKS_MAX template. One of the callback, to be more specific *_compute_max(), calculates a maximum scalar value of node against its left/right sub-tree. To simplify the code and improve readability we can switch and make use of max3() macro that makes the code more transparent. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> --- include/linux/rbtree_augmented.h | 40 +++++++++++++++++----------------- tools/include/linux/rbtree_augmented.h | 40 +++++++++++++++++----------------- 2 files changed, 40 insertions(+), 40 deletions(-)