linux-kernel - [PATCH 2/3] clocksource: exynos

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Message-Id: <1401903034-20074-2-git-send-email-dianders@chromium.org>
Date:	Wed,  4 Jun 2014 10:30:33 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Kukjin Kim <kgene.kim@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Chirantan Ekbote <chirantan@...omium.org>,
	David Riley <davidriley@...omium.org>, olof@...om.net,
	linux-samsung-soc@...r.kernel.org,
	Mandeep Singh Baines <msb@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Doug Anderson <dianders@...omium.org>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 2/3] clocksource: exynos_mct: cache mct upper count

From: Mandeep Singh Baines <msb@...omium.org>

Saves one register read.  Note that the upper count only changes every
~178 seconds with a 24MHz source clock, so it's likely it hasn't
changed from call to call.

Before: 1323852 us for 1000000 gettimeofday in userspace
After:  1173084 us for 1000000 gettimeofday in userspace

Note that even with this change the CPU is in exynos_frc_read() more
than 2% of the time in real world profiles of ChromeOS.  That
indicates that it's important to optimize.

Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
Signed-off-by: Doug Anderson <dianders@...omium.org>
---
 drivers/clocksource/exynos_mct.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index ba3a683..7cbe4aa 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -167,8 +167,8 @@ static void exynos4_mct_frc_start(u32 hi, u32 lo)
 
 static inline cycle_t notrace _exynos4_frc_read(void)
 {
-	unsigned int lo, hi;
-	u32 hi2 = __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_U);
+	u32 lo, hi;
+	static u32 hi2;
 
 	do {
 		hi = hi2;
-- 
2.0.0.526.g5318336

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