2013-02-22 16:28:51

by Felix Fietkau

Subject: [PATCH] ieee80211: mark 802.11 related structs as being 2-byte aligned

Regardless of what header features they use, or if they align the IP
header or not, 802.11 packets from all drivers guarantee a 2-byte
alignment (and there's a debug WARN_ON in case they don't).

Annotate packet structs with __aligned(2) to allow the compiler to use
16-bit load/store operations on platforms with extremely inefficient
unaligned access (e.g. MIPS).

This reduces code size and improves performance on affected platforms
and causes no binary code change on others.

Signed-off-by: Felix Fietkau <[email protected]>
---
include/linux/ieee80211.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
index 7e24fe0..bbccc2e 100644
--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -185,7 +185,7 @@ struct ieee80211_hdr {
u8 addr3[6];
__le16 seq_ctrl;
u8 addr4[6];
-} __packed;
+} __packed __aligned(2);

struct ieee80211_hdr_3addr {
__le16 frame_control;
@@ -194,7 +194,7 @@ struct ieee80211_hdr_3addr {
u8 addr2[6];
u8 addr3[6];
__le16 seq_ctrl;
-} __packed;
+} __packed __aligned(2);

struct ieee80211_qos_hdr {
__le16 frame_control;
@@ -204,7 +204,7 @@ struct ieee80211_qos_hdr {
u8 addr3[6];
__le16 seq_ctrl;
__le16 qos_ctrl;
-} __packed;
+} __packed __aligned(2);

/**
* ieee80211_has_tods - check if IEEE80211_FCTL_TODS is set
@@ -581,7 +581,7 @@ struct ieee80211s_hdr {
__le32 seqnum;
u8 eaddr1[6];
u8 eaddr2[6];
-} __packed;
+} __packed __aligned(2);

/* Mesh flags */
#define MESH_FLAGS_AE_A4 0x1
@@ -875,7 +875,7 @@ struct ieee80211_mgmt {
} u;
} __packed action;
} u;
-} __packed;
+} __packed __aligned(2);

/* Supported Rates value encodings in 802.11n-2009 7.3.2.2 */
#define BSS_MEMBERSHIP_SELECTOR_HT_PHY 127
@@ -906,20 +906,20 @@ struct ieee80211_rts {
__le16 duration;
u8 ra[6];
u8 ta[6];
-} __packed;
+} __packed __aligned(2);

struct ieee80211_cts {
__le16 frame_control;
__le16 duration;
u8 ra[6];
-} __packed;
+} __packed __aligned(2);

struct ieee80211_pspoll {
__le16 frame_control;
__le16 aid;
u8 bssid[6];
u8 ta[6];
-} __packed;
+} __packed __aligned(2);

/* TDLS */

--
1.8.0.2

2013-02-22 20:24:37

by Johannes Berg

Subject: Re: [PATCH] ieee80211: mark 802.11 related structs as being 2-byte aligned

On Fri, 2013-02-22 at 17:28 +0100, Felix Fietkau wrote:
> Regardless of what header features they use, or if they align the IP
> header or not, 802.11 packets from all drivers guarantee a 2-byte
> alignment (and there's a debug WARN_ON in case they don't).
>
> Annotate packet structs with __aligned(2) to allow the compiler to use
> 16-bit load/store operations on platforms with extremely inefficient
> unaligned access (e.g. MIPS).
>
> This reduces code size and improves performance on affected platforms
> and causes no binary code change on others.

Applied.

johannes