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Subject[tip: sched/core] sched: Fill unconditional hole induced by sched_entity
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 804bccba71a57e7e5deb507a4c8ebbab730909c0
Gitweb: https://git.kernel.org/tip/804bccba71a57e7e5deb507a4c8ebbab730909c0
Author: Kees Cook <keescook@chromium.org>
AuthorDate: Thu, 23 Sep 2021 19:54:50 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 14 Oct 2021 13:09:58 +02:00

sched: Fill unconditional hole induced by sched_entity

With struct sched_entity before the other sched entities, its alignment
won't induce a struct hole. This saves 64 bytes in defconfig task_struct:

Before:
...
unsigned int rt_priority; /* 120 4 */

/* XXX 4 bytes hole, try to pack */

/* --- cacheline 2 boundary (128 bytes) --- */
const struct sched_class * sched_class; /* 128 8 */

/* XXX 56 bytes hole, try to pack */

/* --- cacheline 3 boundary (192 bytes) --- */
struct sched_entity se __attribute__((__aligned__(64))); /* 192 448 */
/* --- cacheline 10 boundary (640 bytes) --- */
struct sched_rt_entity rt; /* 640 48 */
struct sched_dl_entity dl __attribute__((__aligned__(8))); /* 688 224 */
/* --- cacheline 14 boundary (896 bytes) was 16 bytes ago --- */

After:
...
unsigned int rt_priority; /* 120 4 */

/* XXX 4 bytes hole, try to pack */

/* --- cacheline 2 boundary (128 bytes) --- */
struct sched_entity se __attribute__((__aligned__(64))); /* 128 448 */
/* --- cacheline 9 boundary (576 bytes) --- */
struct sched_rt_entity rt; /* 576 48 */
struct sched_dl_entity dl __attribute__((__aligned__(8))); /* 624 224 */
/* --- cacheline 13 boundary (832 bytes) was 16 bytes ago --- */

Summary diff:
- /* size: 7040, cachelines: 110, members: 188 */
+ /* size: 6976, cachelines: 109, members: 188 */

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210924025450.4138503-1-keescook@chromium.org
---
include/linux/sched.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 193e16e..343603f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -775,10 +775,10 @@ struct task_struct {
int normal_prio;
unsigned int rt_priority;

- const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
struct sched_dl_entity dl;
+ const struct sched_class *sched_class;

#ifdef CONFIG_SCHED_CORE
struct rb_node core_node;
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