Re: [PATCH block:for-3.3/core] block: disable ELEVATOR_INSERT_SORT_MERGE

From: Tejun Heo
Date: Thu Jan 05 2012 - 23:38:37 EST


On Thu, Jan 5, 2012 at 8:19 PM, Shaohua Li <> wrote:
>> For detailed discussion of the bug:
> this is overkill. when plug is added, we found huge performance
> regression, that's why we add INSERT_SORT_MERGE.

With what workload? I suspect most of the improvements is from merging
across different cfqqs, no? The whole recursive thing can't be very
useful if cross-cfqq merging isn't allowed. Maybe there are specific
cases where last_merge hint merging can be specially effective. I
don't know. Regardless, this is an apparent bug and the block tree
will be pushed mainline pretty soon. If necessary, fix it better
later. Doing complex things inside merge window usually isn't a good


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