linux-kernel - Re: [PATCH v2] wait while adding MMC host to ensure root mounts

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Date:	Thu, 04 Apr 2013 09:35:58 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Sergey Yanovich <ynvich@...il.com>
CC:	Chris Ball <cjb@...top.org>, Ulf Hansson <ulf.hansson@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Namjae Jeon <linkinjeon@...il.com>,
	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v2] wait while adding MMC host to ensure root mounts

On 02/04/13 17:24, Sergey Yanovich wrote:
> On Tue, 2013-04-02 at 16:36 +0300, Adrian Hunter wrote:
>> On my system it is significant:
>>
>> Before the patch:
>>
>> [    1.625623] VFS: Mounted root (ext4 filesystem) readonly on device 179:2.
>>
>> After the patch:
>>
>> [    1.935851] VFS: Mounted root (ext4 filesystem) readonly on device 179:2.
>>
>> That is an addition of 310 ms which is 19% performance degradation.
> 
> Are you sure the delay is caused by mmc?

Yes

> 
> On my intel laptop (userspace is Debian/unstable):
> [    1.542339] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)
> ...
> [    2.735851] mmc0: new high speed SD card at address e624
> [    2.742289] mmcblk0: mmc0:e624 SU02G 1.84 GiB 
> [    2.752317]  mmcblk0: p1


No,  I am booting from eMMC.

> 
>> Please revert the patch.
> 
> Chris, could provide a pointer on how to improve the patch?
> 
> Maybe introduce mmc_is_hosting_root() and do something like:
> 
> -	mmc_flush_scheduled_work();
> +	if (mmc_is_hosting_root())
> +		mmc_flush_scheduled_work();

No, I am booting from eMMC.  Perhaps a host capability:

	if (host->caps2 & MMC_CAP2_ROOTWAIT)
		mmc_flush_scheduled_work();

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