linux-kernel - [PATCH v5 02/18] drivers/net/b44: Align pwol_mask to unsigned long for better performance

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Date:   Tue, 12 Mar 2019 16:00:20 -0700
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>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Xiaoyao Li " <xiaoyao.li@...el.com>,
        "Michael Chan" <michael.chan@...adcom.com>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, kvm@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v5 02/18] drivers/net/b44: Align pwol_mask to unsigned long for better performance

From: Peter Zijlstra <peterz@...radead.org>

A bit in pwol_mask is set in b44_magic_pattern by atomic set_bit.
But since pwol_mask is local and never exposed to concurrency, there is
no need to set bit in pwol_mask atomically.

set_bit sets the bit in a single unsigned long location. Because 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.

So we use non atomic __set_bit to set pwol_mask bits. __set_bit won't
hit split lock issue on x86.

Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 drivers/net/ethernet/broadcom/b44.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
index 97ab0dd25552..5738ab963dfb 100644
--- a/drivers/net/ethernet/broadcom/b44.c
+++ b/drivers/net/ethernet/broadcom/b44.c
@@ -1520,7 +1520,7 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset)
 
 	memset(ppattern + offset, 0xff, magicsync);
 	for (j = 0; j < magicsync; j++)
-		set_bit(len++, (unsigned long *) pmask);
+		__set_bit(len++, (unsigned long *)pmask);
 
 	for (j = 0; j < B44_MAX_PATTERNS; j++) {
 		if ((B44_PATTERN_SIZE - len) >= ETH_ALEN)
@@ -1532,7 +1532,7 @@ static int b44_magic_pattern(u8 *macaddr, u8 *ppattern, u8 *pmask, int offset)
 		for (k = 0; k< ethaddr_bytes; k++) {
 			ppattern[offset + magicsync +
 				(j * ETH_ALEN) + k] = macaddr[k];
-			set_bit(len++, (unsigned long *) pmask);
+			__set_bit(len++, (unsigned long *)pmask);
 		}
 	}
 	return len - 1;
-- 
2.19.1