[tip: sched/core] sched: Fill unconditional hole induced by sched_entity

["tip-bot2 for Kees Cook" <tip-bot2@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxx>
AuthorDate:    Thu, 23 Sep 2021 19:54:50 -07:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210924025450.4138503-1-keescook@xxxxxxxxxxxx
---
 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;