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

[Tejun Heo]

Hello,

On Thu, Jan 5, 2012 at 8:19 PM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote:
>> For detailed discussion of the bug:
>>
>>  http://thread.gmane.org/gmane.linux.kernel.next/20064/focus=20159
>>
> 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
idea.

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/