[PATCH] block/ps3: Fix slow VRAM IO

From: Geoff Levand <geoffrey.levand@am.sony.com>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Jim Paris <jim@jtan.com>,
	Cell Broadband Engine OSS Development  <cbe-oss-dev@ozlabs.org>,
	Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] block/ps3: Fix slow VRAM IO
Date: Mon, 19 Oct 2009 12:58:27 -0700	[thread overview]
Message-ID: <4ADCC4E3.8060104@am.sony.com> (raw)


From: Hideyuki Sasaki <Hideyuki_Sasaki@hq.scei.sony.co.jp>

The current PS3 VRAM driver uses msleep() to wait for completion
of RSX DMA transfers between system memory and VRAM.  Depending
on the system timing, the processing delay and overhead of this
msleep() call can significantly impact VRAM driver IO.

To avoid the condition, add a short duration (200 usec max)
udelay() polling loop before entering the msleep() polling
loop.

Signed-off-by: Hideyuki Sasaki <xhide@rd.scei.sony.co.jp>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
---

 drivers/block/ps3vram.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/block/ps3vram.c
+++ b/drivers/block/ps3vram.c
@@ -123,7 +123,15 @@ static int ps3vram_notifier_wait(struct 
 {
 	struct ps3vram_priv *priv = ps3_system_bus_get_drvdata(dev);
 	u32 *notify = ps3vram_get_notifier(priv->reports, NOTIFIER);
-	unsigned long timeout = jiffies + msecs_to_jiffies(timeout_ms);
+	unsigned long timeout;
+
+	for (timeout = 20; timeout; timeout--) {
+		if (!notify[3])
+			return 0;
+		udelay(10);
+	}
+
+	timeout = jiffies + msecs_to_jiffies(timeout_ms);
 
 	do {
 		if (!notify[3])

