linux-kernel - RE: [PATCH] OMAP: HSMMC: Do not enable buffer ready interrupt if using DMA

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Date:	Wed, 6 May 2009 13:31:29 +0530
From:	"Gadiyar, Anand" <gadiyar@...com>
To:	Jarkko Lavinen <jarkko.lavinen@...ia.com>
CC:	"pierre@...man.eu" <pierre@...man.eu>,
	Tony Lindgren <tony@...mide.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: RE: [PATCH] OMAP: HSMMC: Do not enable buffer ready interrupt if
	using DMA

On Tue, May 5, 2009, Jarkko Lavinen wrote: 
> On Tue, Apr 21, 2009 at 09:39:22AM +0200, ext Gadiyar, Anand wrote:
> > From: Anand Gadiyar <gadiyar@...com>
> > 
> > OMAP: HSMMC: Do not enable buffer ready interrupt if using DMA
> > 
> > This considerably reduces the number of interrupts during a transfer
> > and ought to result in some power saving.
> 
> I tried the patch with reading from the raw mmc block device to
> /dev/null with dd (with bs 32k and 1M).  I cannot see any
> difference in interrupt count from /proc/interrupts or in read
> speed. At least the patch works. Cpu was 34340es3.
> 
> I also trid without the patch just disabling the Buffer
> Read/write Ready bits from INT_EN_MASK which is then written to
> both MMCHS_IE and MMCHS_ISE.  Still no change in read speed nor
> mmc irq count.
> 
> Cheers
> Jarkko Lavinen

I discovered this while doing MMC writes. I did not check if there
was any difference during a read. I notice you have only tested with
MMC reads.

Here's what I get with and without the patch.

- Anand

Without patch
/ # mount -t vfat /dev/mmcblk0 /mnt/mmc
/ # cat /proc/interrupts | grep mmc
 83:         90        INTC  mmc0
384:          1     twl4030  mmc0
/ # dd if=/dev/zero of=/mnt/mmc/32kbs.txt bs=32k count=1000
1000+0 records in
1000+0 records out
/ # cat /proc/interrupts | grep mmc
 83:       3760        INTC  mmc0
384:          1     twl4030  mmc0
/ # dd if=/dev/zero of=/mnt/mmc/1Mbs.txt bs=1M count=32
32+0 records in
32+0 records out
/ # cat /proc/interrupts | grep mmc
 83:       7570        INTC  mmc0
384:          1     twl4030  mmc0
/ # ls -l /mnt/mmc
-rwxr-xr-x    1 root     root     33554432 Dec 31 18:03 1Mbs.txt
-rwxr-xr-x    1 root     root     32768000 Dec 31 18:03 32kbs.txt
/ # umount /mnt/mmc


With patch
/ # mount -t vfat /dev/mmcblk0 /mnt/mmc
/ # cat /proc/interrupts | grep mmc
 83:         67        INTC  mmc0
384:          0     twl4030  mmc0
/ # dd if=/dev/zero of=/mnt/mmc/32kbs.txt bs=32k count=1000
1000+0 records in
1000+0 records out
/ # cat /proc/interrupts | grep mmc
 83:       3103        INTC  mmc0
384:          0     twl4030  mmc0
/ # dd if=/dev/zero of=/mnt/mmc/1Mbs.txt bs=1M count=32
32+0 records in
32+0 records out
/ # cat /proc/interrupts | grep mmc
 83:       6170        INTC  mmc0
384:          0     twl4030  mmc0
/ # ls -l /mnt/mmc
-rwxr-xr-x    1 root     root     33554432 Dec 31 18:01 1Mbs.txt
-rwxr-xr-x    1 root     root     32768000 Dec 31 18:00 32kbs.txt
/ # umount /mnt/mmc--
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