linux-kernel - [PATCH v4 03/17] wlcore: Align reg_ch_conf_pending and tmp_ch_bitmap to unsigned long for better performance

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Date:   Fri,  1 Mar 2019 18:44:57 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "H Peter Anvin" <hpa@...or.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        "Xiaoyao Li " <xiaoyao.li@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, kvm@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v4 03/17] wlcore: Align reg_ch_conf_pending and tmp_ch_bitmap to unsigned long for better performance

A bit in reg_ch_conf_pending in wl271 and tmp_ch_bitmap is set atomically
by set_bit(). set_bit() sets the bit in a single unsigned long location. If
the variables are not aligned to unsigned long, set_bit() accesses two
cache lines and thus causes slower performance. On x86, this scenario is
called split lock and can cause overall performance degradation due to
locked BTSL instruction in set_bit() locks bus.

To avoid performance degradation, the two variables are aligned to
unsigned long.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 drivers/net/wireless/ti/wlcore/cmd.c    | 3 ++-
 drivers/net/wireless/ti/wlcore/wlcore.h | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/ti/wlcore/cmd.c b/drivers/net/wireless/ti/wlcore/cmd.c
index 903968735a74..8d15a6307d44 100644
--- a/drivers/net/wireless/ti/wlcore/cmd.c
+++ b/drivers/net/wireless/ti/wlcore/cmd.c
@@ -1707,7 +1707,8 @@ int wlcore_cmd_regdomain_config_locked(struct wl1271 *wl)
 {
 	struct wl12xx_cmd_regdomain_dfs_config *cmd = NULL;
 	int ret = 0, i, b, ch_bit_idx;
-	u32 tmp_ch_bitmap[2];
+	/* Align to unsigned long for better performance in set_bit() */
+	u32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));
 	struct wiphy *wiphy = wl->hw->wiphy;
 	struct ieee80211_supported_band *band;
 	bool timeout = false;
diff --git a/drivers/net/wireless/ti/wlcore/wlcore.h b/drivers/net/wireless/ti/wlcore/wlcore.h
index dd14850b0603..92d878f01fa5 100644
--- a/drivers/net/wireless/ti/wlcore/wlcore.h
+++ b/drivers/net/wireless/ti/wlcore/wlcore.h
@@ -321,8 +321,10 @@ struct wl1271 {
 
 	/* Reg domain last configuration */
 	u32 reg_ch_conf_last[2]  __aligned(8);
-	/* Reg domain pending configuration */
-	u32 reg_ch_conf_pending[2];
+	/* Reg domain pending configuration. Aligned to unsigned long for
+	 * better performane in set_bit().
+	 */
+	u32 reg_ch_conf_pending[2] __aligned(sizeof(unsigned long));
 
 	/* Pointer that holds DMA-friendly block for the mailbox */
 	void *mbox;
-- 
2.7.4