Re: [PATCH]block: Observing higher CPU utilization during random IO testing

[Ming Lei <tom.leiming@gmail.com>]

On Thu, Jun 04, 2026 at 12:27:09PM -0400, wenxiong@linux.ibm.com wrote:
> From: Wen Xiong <wenxiong@linux.ibm.com>
> 
> Hi All,
> 
> Our performance team observed the higher CPU utilization in RHEL10 compared
> to RHEL9.8, observed the similar issue in upstream kernel(v7.1-rc6) as well
> when running FIO random IO tests. Random IO tests are more CPU intensive
> than sequential IO tests due to several factors: more context switching,
> interrupt Handling, cache Inefficiency etc.
> 
> Given commit 060406c61c7c ("block: add plug while submitting IO")
> causes performance regression. This patch reverts it.

One thing is that plugging should be applied in outer io code path, also
it doesn't make sense to apply this timestamp optimization for single IO batch.

> 
> Below is performance comparison with the latest upstream kernel.
> 
> Iotype  qd   nj    rmix    mpstat busy        mpstat busy
>                          with inner plug    without inner plug
> Randrw  1    20    100       53%                 24%
> Randrw  1    40    100       70%                 24%
> Randrw  1    20    70        40%                 24%
> Randrw  1    40    70        60%                 26%
> Randrw  1    20    0         14%                 6%
> Randrw  1    40    0         20%                 7%
> 
> Signed-off-by: Wen Xiong <wenxiong@linux.ibm.com>
> Suggested-by: Ming Lei <tom.leiming@gmail.com>

With commit log update, this patch looks fine:

Reviewed-by: Ming Lei <tom.leiming@gmail.com>


Thanks,
Ming