linux-kernel - [PATCH v5 2/2] mmc: core: Optimize the mmc erase size alignment

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Message-Id: <bc52ccbc0c22e2d2f795d75faf748e4e68900e51.1473215578.git.baolin.wang@linaro.org>
Date:   Wed,  7 Sep 2016 10:38:25 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     ulf.hansson@...aro.org
Cc:     adrian.hunter@...el.com, rmk+kernel@....linux.org.uk,
        shawn.lin@...k-chips.com, dianders@...omium.org, heiko@...ech.de,
        david@...tonic.nl, hdegoede@...hat.com, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, broonie@...nel.org,
        linus.walleij@...aro.org, baolin.wang@...aro.org
Subject: [PATCH v5 2/2] mmc: core: Optimize the mmc erase size alignment

In most cases the 'card->erase_size' is power of 2, then the round_up/down()
function is more efficient than '%' operation when the 'card->erase_size' is
power of 2.

Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
Tested-by: Shawn Lin <shawn.lin@...k-chips.com>
---
 drivers/mmc/core/core.c |   34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 11b4897..4264ac6 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2209,19 +2209,37 @@ static unsigned int mmc_align_erase_size(struct mmc_card *card,
 {
 	unsigned int from_new = *from, nr_new = nr, rem;
 
-	rem = from_new % card->erase_size;
-	if (rem) {
-		rem = card->erase_size - rem;
-		from_new += rem;
+	/*
+	 * When the 'card->erase_size' is power of 2, we can use round_up/down()
+	 * to align the erase size efficiently.
+	 */
+	if (is_power_of_2(card->erase_size)) {
+		unsigned int temp = from_new;
+
+		from_new = round_up(temp, card->erase_size);
+		rem = from_new - temp;
+
 		if (nr_new > rem)
 			nr_new -= rem;
 		else
 			return 0;
-	}
 
-	rem = nr_new % card->erase_size;
-	if (rem)
-		nr_new -= rem;
+		nr_new = round_down(nr_new, card->erase_size);
+	} else {
+		rem = from_new % card->erase_size;
+		if (rem) {
+			rem = card->erase_size - rem;
+			from_new += rem;
+			if (nr_new > rem)
+				nr_new -= rem;
+			else
+				return 0;
+		}
+
+		rem = nr_new % card->erase_size;
+		if (rem)
+			nr_new -= rem;
+	}
 
 	if (nr_new == 0)
 		return 0;
-- 
1.7.9.5