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Message-Id: <a804f2e91bc32cc5e17e012ed90972415606db4e.1687075665.git.christophe.jaillet@wanadoo.fr>
Date: Sun, 18 Jun 2023 10:08:07 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Jiri Kosina <jikos@...nel.org>,
Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
linux-input@...r.kernel.org
Subject: [PATCH] HID: Reorder fields in 'struct hid_field'
Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct hid_field'
from 136 to 128 bytes.
It saves a few bytes of memory and is more cache-line friendly.
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
Using pahole
Before:
======
struct hid_field {
unsigned int physical; /* 0 4 */
unsigned int logical; /* 4 4 */
unsigned int application; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
struct hid_usage * usage; /* 16 8 */
unsigned int maxusage; /* 24 4 */
unsigned int flags; /* 28 4 */
unsigned int report_offset; /* 32 4 */
unsigned int report_size; /* 36 4 */
unsigned int report_count; /* 40 4 */
unsigned int report_type; /* 44 4 */
__s32 * value; /* 48 8 */
__s32 * new_value; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
__s32 * usages_priorities; /* 64 8 */
__s32 logical_minimum; /* 72 4 */
__s32 logical_maximum; /* 76 4 */
__s32 physical_minimum; /* 80 4 */
__s32 physical_maximum; /* 84 4 */
__s32 unit_exponent; /* 88 4 */
unsigned int unit; /* 92 4 */
bool ignored; /* 96 1 */
/* XXX 7 bytes hole, try to pack */
struct hid_report * report; /* 104 8 */
unsigned int index; /* 112 4 */
/* XXX 4 bytes hole, try to pack */
struct hid_input * hidinput; /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
__u16 dpad; /* 128 2 */
/* XXX 2 bytes hole, try to pack */
unsigned int slot_idx; /* 132 4 */
/* size: 136, cachelines: 3, members: 25 */
/* sum members: 119, holes: 4, sum holes: 17 */
/* last cacheline: 8 bytes */
};
After:
=====
struct hid_field {
unsigned int physical; /* 0 4 */
unsigned int logical; /* 4 4 */
unsigned int application; /* 8 4 */
/* XXX 4 bytes hole, try to pack */
struct hid_usage * usage; /* 16 8 */
unsigned int maxusage; /* 24 4 */
unsigned int flags; /* 28 4 */
unsigned int report_offset; /* 32 4 */
unsigned int report_size; /* 36 4 */
unsigned int report_count; /* 40 4 */
unsigned int report_type; /* 44 4 */
__s32 * value; /* 48 8 */
__s32 * new_value; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
__s32 * usages_priorities; /* 64 8 */
__s32 logical_minimum; /* 72 4 */
__s32 logical_maximum; /* 76 4 */
__s32 physical_minimum; /* 80 4 */
__s32 physical_maximum; /* 84 4 */
__s32 unit_exponent; /* 88 4 */
unsigned int unit; /* 92 4 */
struct hid_report * report; /* 96 8 */
unsigned int index; /* 104 4 */
bool ignored; /* 108 1 */
/* XXX 3 bytes hole, try to pack */
struct hid_input * hidinput; /* 112 8 */
__u16 dpad; /* 120 2 */
/* XXX 2 bytes hole, try to pack */
unsigned int slot_idx; /* 124 4 */
/* size: 128, cachelines: 2, members: 25 */
/* sum members: 119, holes: 3, sum holes: 9 */
};
---
include/linux/hid.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 39e21e3815ad..5be5e671c263 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -480,9 +480,9 @@ struct hid_field {
__s32 physical_maximum;
__s32 unit_exponent;
unsigned unit;
- bool ignored; /* this field is ignored in this event */
struct hid_report *report; /* associated report */
unsigned index; /* index into report->field[] */
+ bool ignored; /* this field is ignored in this event */
/* hidinput data */
struct hid_input *hidinput; /* associated input structure */
__u16 dpad; /* dpad input code */
--
2.34.1
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