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Message-Id: <6b868520dac20434296b6282496d3234fae01115.1676631473.git.christophe.jaillet@wanadoo.fr>
Date: Fri, 17 Feb 2023 11:59:08 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <lenb@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
linux-acpi@...r.kernel.org
Subject: [PATCH] ACPI: video: Reorder fields in 'struct acpi_video_device'
Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct acpi_video_device'
from 264 to 256 bytes.
This size is much better when the struct is kmalloc()'ed.
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
Using pahole
Before:
======
struct acpi_video_device {
long unsigned int device_id; /* 0 8 */
struct acpi_video_device_flags flags; /* 8 1 */
struct acpi_video_device_cap cap; /* 9 1 */
/* XXX 6 bytes hole, try to pack */
struct list_head entry; /* 16 16 */
struct delayed_work switch_brightness_work; /* 32 184 */
/* XXX last struct has 4 bytes of padding */
/* --- cacheline 3 boundary (192 bytes) was 24 bytes ago --- */
int switch_brightness_event; /* 216 4 */
/* XXX 4 bytes hole, try to pack */
struct acpi_video_bus * video; /* 224 8 */
struct acpi_device * dev; /* 232 8 */
struct acpi_video_device_brightness * brightness; /* 240 8 */
struct backlight_device * backlight; /* 248 8 */
/* --- cacheline 4 boundary (256 bytes) --- */
struct thermal_cooling_device * cooling_dev; /* 256 8 */
/* size: 264, cachelines: 5, members: 11 */
/* sum members: 254, holes: 2, sum holes: 10 */
/* paddings: 1, sum paddings: 4 */
/* last cacheline: 8 bytes */
};
After:
=====
struct acpi_video_device {
long unsigned int device_id; /* 0 8 */
struct list_head entry; /* 8 16 */
struct acpi_video_device_flags flags; /* 24 1 */
struct acpi_video_device_cap cap; /* 25 1 */
/* XXX 2 bytes hole, try to pack */
int switch_brightness_event; /* 28 4 */
struct delayed_work switch_brightness_work; /* 32 184 */
/* XXX last struct has 4 bytes of padding */
/* --- cacheline 3 boundary (192 bytes) was 24 bytes ago --- */
struct acpi_video_bus * video; /* 216 8 */
struct acpi_device * dev; /* 224 8 */
struct acpi_video_device_brightness * brightness; /* 232 8 */
struct backlight_device * backlight; /* 240 8 */
struct thermal_cooling_device * cooling_dev; /* 248 8 */
/* size: 256, cachelines: 4, members: 11 */
/* sum members: 254, holes: 1, sum holes: 2 */
/* paddings: 1, sum paddings: 4 */
};
---
drivers/acpi/acpi_video.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 97b711e57bff..1118dd7dbf6c 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -202,11 +202,11 @@ struct acpi_video_device_cap {
struct acpi_video_device {
unsigned long device_id;
+ struct list_head entry;
struct acpi_video_device_flags flags;
struct acpi_video_device_cap cap;
- struct list_head entry;
- struct delayed_work switch_brightness_work;
int switch_brightness_event;
+ struct delayed_work switch_brightness_work;
struct acpi_video_bus *video;
struct acpi_device *dev;
struct acpi_video_device_brightness *brightness;
--
2.34.1
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