Re: [PATCH] block: don't quiesce the queue when setting the default elevator

[Qiliang Yuan]

Hi Ming, Jens,

Gentle ping. Since 1e44bedbc921 ("block: unifying elevator change"),
setting the default elevator quiesces the queue again, which
245a489e81e1 had avoided, so every disk added with a default elevator
waits for an RCU grace period. START_DEV of a single-queue ublk device
takes 7.74ms at p50 instead of 0.68ms.

Ming, as the author of 1e44bedbc921, could you take a look when you
have a moment?

Thanks,
Qiliang