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

[Adrian Hunter <adrian.hunter@intel.com>]

On 27/03/13 13:57, Chris Ball wrote:
> Hi,
> 
> On Wed, Mar 27 2013, Ulf Hansson wrote:
>> I noticed you merged this. I thought the idea was to use the rootwait
>> or rootdelay?
> 
> That's necessary before the patch, but it would be better if we didn't
> have to pass rootwait, all else being equal.
> 
>> Moreover, this patch will have bad impact on booting the kernel, since
>> every host device that has scheduled a detect work from it's probe
>> function will also wait for it to finish. Even if it is the boot
>> device of not. If this is needed, I would prefer that a host cap is
>> used.
> 
> I see, you're worried about a performance regression where every boot
> takes longer than it used to while MMC quiesces.  That's fair.  Do you
> think you could tell me how much delay this adds to a boot for you, so
> that we can consider whether the usability improvement is worth it?
> 
> If the delay's significant, I agree with you and will revert this patch.

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.

Please revert the patch.