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




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