git: 5d91386826d0 - main - rb_tree: avoid extra reads in rebalancing
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Date: Mon, 29 Aug 2022 16:13:52 UTC
The branch main has been updated by dougm:
URL: https://cgit.FreeBSD.org/src/commit/?id=5d91386826d0f360d87ce3f39c9ebf266f149325
commit 5d91386826d0f360d87ce3f39c9ebf266f149325
Author: Doug Moore <dougm@FreeBSD.org>
AuthorDate: 2022-08-29 16:11:31 +0000
Commit: Doug Moore <dougm@FreeBSD.org>
CommitDate: 2022-08-29 16:11:31 +0000
rb_tree: avoid extra reads in rebalancing
In RB_INSERT_COLOR and RB_REMOVE_COLOR, avoid reading a parent pointer
from memory, and then reading the left-color bit from memory, and then
reading the right-color bit from memory, since they're all in the same
field. The compiler can't infer that only the first read is really
necessary, so write the code in a way so that it doesn't have to.
Drop RB_RED_LEFT and RB_RED_RIGHT macros that reach into memory to get
those bits. Drop RB_COLOR, the only thing left using RB_RED_LEFT and
RB_RED_RIGHT after the other changes, and go straight to DIAGNOSTIC
code in subr_stats to implement RB_COLOR for its single, dubious use
there.
Reviewed by: alc
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D36353
---
sys/kern/subr_stats.c | 9 +++++-
sys/sys/tree.h | 82 +++++++++++++++++++++++++++------------------------
2 files changed, 52 insertions(+), 39 deletions(-)
diff --git a/sys/kern/subr_stats.c b/sys/kern/subr_stats.c
index 946999263898..0984d2a21014 100644
--- a/sys/kern/subr_stats.c
+++ b/sys/kern/subr_stats.c
@@ -3406,6 +3406,13 @@ stats_v1_vsd_tdgst_add(enum vsd_dtype vs_dtype, struct voistatdata_tdgst *tdgst,
Q_TOSTR(rbctd64->mu, -1, 10, qstr,
sizeof(qstr));
+ struct voistatdata_tdgstctd64 *parent;
+ parent = RB_PARENT(rbctd64, rblnk);
+ int rb_color =
+ parent == NULL ? 0 :
+ RB_LEFT(parent, rblnk) == rbctd64 ?
+ (RB_BITS(parent, rblnk) & RB_RED_L) != 0 :
+ (RB_BITS(parent, rblnk) & RB_RED_R) != 0;
printf(" RB ctd=%3d p=%3d l=%3d r=%3d c=%2d "
"mu=%s\n",
(int)ARB_SELFIDX(ctd64tree, rbctd64),
@@ -3415,7 +3422,7 @@ stats_v1_vsd_tdgst_add(enum vsd_dtype vs_dtype, struct voistatdata_tdgst *tdgst,
RB_LEFT(rbctd64, rblnk)),
(int)ARB_SELFIDX(ctd64tree,
RB_RIGHT(rbctd64, rblnk)),
- RB_COLOR(rbctd64, rblnk),
+ rb_color,
qstr);
panic("RB@%p and ARB@%p trees differ\n",
diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index bd804c1a64db..971562a5c121 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -341,8 +341,6 @@ struct { \
#define RB_FLIP_LEFT(elm, field) (RB_BITS(elm, field) ^= RB_RED_L)
#define RB_FLIP_RIGHT(elm, field) (RB_BITS(elm, field) ^= RB_RED_R)
#define RB_FLIP_ALL(elm, field) (RB_BITS(elm, field) ^= RB_RED_MASK)
-#define RB_RED_LEFT(elm, field) ((RB_BITS(elm, field) & RB_RED_L) != 0)
-#define RB_RED_RIGHT(elm, field) ((RB_BITS(elm, field) & RB_RED_R) != 0)
#define _RB_PARENT_ONLY(elm) (__typeof(elm)) \
((__uintptr_t)elm & ~RB_RED_MASK)
#define RB_PARENT(elm, field) _RB_PARENT_ONLY(RB_UP(elm, field))
@@ -359,11 +357,6 @@ struct { \
RB_LEFT(elm, field) = RB_RIGHT(elm, field) = NULL; \
} while (/*CONSTCOND*/ 0)
-#define RB_COLOR(elm, field) (RB_PARENT(elm, field) == NULL ? 0 : \
- RB_LEFT(RB_PARENT(elm, field), field) == elm ? \
- RB_RED_LEFT(RB_PARENT(elm, field), field) : \
- RB_RED_RIGHT(RB_PARENT(elm, field), field))
-
/*
* Something to be invoked in a loop at the root of every modified subtree,
* from the bottom up to the root, to update augmented node data.
@@ -489,67 +482,72 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
* when a value has been assigned to 'child' in the previous \
* one. \
*/ \
- struct type *child, *gpar, *parent; \
- while ((parent = RB_PARENT(elm, field)) != NULL) { \
- gpar = RB_PARENT(parent, field); \
+ struct type *child, *gpar = RB_UP(elm, field), *parent; \
+ __uintptr_t red; \
+ \
+ while ((parent = gpar) != NULL) { \
+ red = RB_BITS(parent, field); \
+ gpar = RB_UP(parent, field); \
if (RB_LEFT(parent, field) == elm) { \
- if (RB_RED_LEFT(parent, field)) { \
+ if (red & RB_RED_L) { \
RB_FLIP_LEFT(parent, field); \
return; \
} \
RB_FLIP_RIGHT(parent, field); \
- if (RB_RED_RIGHT(parent, field)) { \
+ if ((red & RB_RED_MASK) == 0) { \
child = elm; \
elm = parent; \
continue; \
} \
- if (RB_RED_RIGHT(elm, field)) \
+ red = RB_BITS(elm, field); \
+ if (red & RB_RED_R) \
child = elm; \
else { \
/* coverity[uninit_use] */ \
RB_ROTATE_LEFT(elm, child, field); \
- if (RB_RED_RIGHT(child, field)) \
+ red = RB_BITS(child, field); \
+ if (red & RB_RED_R) \
RB_FLIP_LEFT(parent, field); \
- if (RB_RED_LEFT(child, field)) \
+ if (red & RB_RED_L) \
RB_FLIP_ALL(elm, field); \
else \
RB_FLIP_LEFT(elm, field); \
- if ((RB_BITS(child, field) & \
- RB_RED_MASK) == 0) \
+ if ((red & RB_RED_MASK) == 0) \
elm = child; \
} \
RB_ROTATE_RIGHT(parent, child, field); \
} else { \
- if (RB_RED_RIGHT(parent, field)) { \
+ if (red & RB_RED_R) { \
RB_FLIP_RIGHT(parent, field); \
return; \
} \
RB_FLIP_LEFT(parent, field); \
- if (RB_RED_LEFT(parent, field)) { \
+ if ((red & RB_RED_MASK) == 0) { \
child = elm; \
elm = parent; \
continue; \
} \
- if (RB_RED_LEFT(elm, field)) \
+ red = RB_BITS(elm, field); \
+ if (red & RB_RED_L) \
child = elm; \
else { \
/* coverity[uninit_use] */ \
RB_ROTATE_RIGHT(elm, child, field); \
- if (RB_RED_LEFT(child, field)) \
+ red = RB_BITS(child, field); \
+ if (red & RB_RED_L) \
RB_FLIP_RIGHT(parent, field); \
- if (RB_RED_RIGHT(child, field)) \
+ if (red & RB_RED_R) \
RB_FLIP_ALL(elm, field); \
else \
RB_FLIP_RIGHT(elm, field); \
- if ((RB_BITS(child, field) & \
- RB_RED_MASK) == 0) \
+ if ((red & RB_RED_MASK) == 0) \
elm = child; \
} \
RB_ROTATE_LEFT(parent, child, field); \
} \
- RB_SET_PARENT(child, gpar, field); \
+ gpar = _RB_PARENT_ONLY(gpar); \
+ RB_UP(child, field) = gpar; \
RB_SWAP_CHILD(head, gpar, parent, child, field); \
- RB_BITS(child, field) &= ~RB_RED_MASK; \
if (elm != child) \
RB_AUGMENT(elm); \
RB_AUGMENT(parent); \
@@ -574,6 +572,8 @@ name##_RB_REMOVE_COLOR(struct name *head, \
struct type *parent, struct type *elm) \
{ \
struct type *gpar, *sib; \
+ __uintptr_t red; \
+ \
if (RB_LEFT(parent, field) == elm && \
RB_RIGHT(parent, field) == elm) { \
RB_BITS(parent, field) &= ~RB_RED_MASK; \
@@ -583,19 +583,21 @@ name##_RB_REMOVE_COLOR(struct name *head, \
return; \
} \
do { \
- gpar = RB_PARENT(parent, field); \
+ red = RB_BITS(parent, field); \
+ gpar = RB_UP(parent, field); \
if (RB_LEFT(parent, field) == elm) { \
- if (!RB_RED_LEFT(parent, field)) { \
+ if (~red & RB_RED_L) { \
RB_FLIP_LEFT(parent, field); \
return; \
} \
- if (RB_RED_RIGHT(parent, field)) { \
+ if ((~red & RB_RED_MASK) == 0) { \
RB_FLIP_RIGHT(parent, field); \
elm = parent; \
continue; \
} \
sib = RB_RIGHT(parent, field); \
- switch (RB_BITS(sib, field) & RB_RED_MASK) { \
+ red = RB_BITS(sib, field); \
+ switch (red & RB_RED_MASK) { \
case RB_RED_MASK: \
RB_FLIP_ALL(sib, field); \
elm = parent; \
@@ -603,11 +605,12 @@ name##_RB_REMOVE_COLOR(struct name *head, \
case RB_RED_R: \
elm = RB_LEFT(sib, field); \
RB_ROTATE_RIGHT(sib, elm, field); \
- if (RB_RED_LEFT(elm, field)) \
+ red = RB_BITS(elm, field); \
+ if (red & RB_RED_L) \
RB_FLIP_ALL(parent, field); \
else \
RB_FLIP_LEFT(parent, field); \
- if (RB_RED_RIGHT(elm, field)) \
+ if (red & RB_RED_R) \
RB_FLIP_ALL(sib, field); \
else \
RB_FLIP_RIGHT(sib, field); \
@@ -629,17 +632,18 @@ name##_RB_REMOVE_COLOR(struct name *head, \
} \
RB_ROTATE_LEFT(parent, elm, field); \
} else { \
- if (!RB_RED_RIGHT(parent, field)) { \
+ if (~red & RB_RED_R) { \
RB_FLIP_RIGHT(parent, field); \
return; \
} \
- if (RB_RED_LEFT(parent, field)) { \
+ if ((~red & RB_RED_MASK) == 0) { \
RB_FLIP_LEFT(parent, field); \
elm = parent; \
continue; \
} \
sib = RB_LEFT(parent, field); \
- switch (RB_BITS(sib, field) & RB_RED_MASK) { \
+ red = RB_BITS(sib, field); \
+ switch (red & RB_RED_MASK) { \
case RB_RED_MASK: \
RB_FLIP_ALL(sib, field); \
elm = parent; \
@@ -647,11 +651,12 @@ name##_RB_REMOVE_COLOR(struct name *head, \
case RB_RED_L: \
elm = RB_RIGHT(sib, field); \
RB_ROTATE_LEFT(sib, elm, field); \
- if (RB_RED_RIGHT(elm, field)) \
+ red = RB_BITS(elm, field); \
+ if (red & RB_RED_R) \
RB_FLIP_ALL(parent, field); \
else \
RB_FLIP_RIGHT(parent, field); \
- if (RB_RED_LEFT(elm, field)) \
+ if (red & RB_RED_L) \
RB_FLIP_ALL(sib, field); \
else \
RB_FLIP_LEFT(sib, field); \
@@ -673,12 +678,13 @@ name##_RB_REMOVE_COLOR(struct name *head, \
} \
RB_ROTATE_RIGHT(parent, elm, field); \
} \
+ gpar = _RB_PARENT_ONLY(gpar); \
RB_SET_PARENT(elm, gpar, field); \
RB_SWAP_CHILD(head, gpar, parent, elm, field); \
if (sib != elm) \
RB_AUGMENT(sib); \
break; \
- } while ((parent = RB_PARENT(elm, field)) != NULL); \
+ } while ((parent = _RB_PARENT_ONLY(gpar)) != NULL); \
}
#define RB_GENERATE_REMOVE(name, type, field, attr) \