linux-kernel - [PATCH v3 02/10] drivers/net/b44: Align pwol_mask to unsigned long for better performance

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Date:   Fri,  1 Feb 2019 21:14:43 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "H Peter Anvin" <hpa@...or.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Michael Chan" <michael.chan@...adcom.com>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        "Ricardo Neri" <ricardo.neri@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v3 02/10] drivers/net/b44: Align pwol_mask to unsigned long for better performance

A bit in pwol_mask is set in b44_magic_pattern automatically by set_bit.
set_bit sets the bit in a single unsigned long location. Since pwol_mask
may not be aligned to unsigned long, the location may cross two cache
lines and accessing the location degradates performance. On x86, accessing
two cache lines in locked instruction in set_bit is called split lock and
can cause overall performance degradation.

To avoid to impact performance by accessing two cache lines in set_bit,
align pwol_mask to unsigned long.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 drivers/net/ethernet/broadcom/b44.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
index 97ab0dd25552..bc544b6b9c3a 100644
--- a/drivers/net/ethernet/broadcom/b44.c
+++ b/drivers/net/ethernet/broadcom/b44.c
@@ -1547,7 +1547,8 @@ static void b44_setup_pseudo_magicp(struct b44 *bp)
 	u32 val;
 	int plen0, plen1, plen2;
 	u8 *pwol_pattern;
-	u8 pwol_mask[B44_PMASK_SIZE];
+	/* Align to unsigned long for better performance in set_bit() */
+	u8 pwol_mask[B44_PMASK_SIZE] __aligned(sizeof(unsigned long));
 
 	pwol_pattern = kzalloc(B44_PATTERN_SIZE, GFP_KERNEL);
 	if (!pwol_pattern)
-- 
2.7.4