[PATCH v8 02/15] drivers/net/b44: Align pwol_mask to unsigned long for better performance

From: Fenghua Yu <fenghua.yu@intel.com>
To: "Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>, "H Peter Anvin" <hpa@zytor.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Dave Hansen" <dave.hansen@intel.com>,
	"Ashok Raj" <ashok.raj@intel.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ravi V Shankar" <ravi.v.shankar@intel.com>,
	"Xiaoyao Li " <xiaoyao.li@intel.com>,
	"Christopherson Sean J" <sean.j.christopherson@intel.com>,
	"Kalle Valo" <kvalo@codeaurora.org>,
	"Michael Chan" <michael.chan@broadcom.com>
Cc: "linux-kernel" <linux-kernel@vger.kernel.org>,
	"x86" <x86@kernel.org>,
	kvm@vger.kernel.org, netdev@vger.kernel.org,
	linux-wireless@vger.kernel.org, Fenghua Yu <fenghua.yu@intel.com>
Subject: [PATCH v8 02/15] drivers/net/b44: Align pwol_mask to unsigned long for better performance
Date: Wed, 24 Apr 2019 12:32:49 -0700	[thread overview]
Message-ID: <1556134382-58814-3-git-send-email-fenghua.yu@intel.com> (raw)
In-Reply-To: <1556134382-58814-1-git-send-email-fenghua.yu@intel.com>

From: Peter Zijlstra <peterz@infradead.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. On x86, accessing two cache lines in locked instruction in
set_bit() is called split locked access and can cause overall performance
degradation.

So 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@infradead.org>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.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

