Re: [PATCH 1/2] block: don't request a module for the none elevator

[Nilay Shroff <nilay@linux.ibm.com>]

On 11/12/26 8:30 AM, Qiliang Yuan wrote:
> elv_iosched_store() calls elv_iosched_load_module() for the requested
> name before anything else, and loads "<name>-iosched" if no elevator
> type of that name is registered. "none" never is, so every write of
> "none" to queue/scheduler ends up in request_module("none-iosched").
> 
> That runs a modprobe helper which can never find the module, and adds
> several milliseconds to every switch to "none", including rewrites of
> it by udev rules or tuning tools that set the scheduler on each disk.
> 
> Return early for "none", like elevator_change() did before the module
> loading moved into elv_iosched_load_module().
> 
> Writing queue/scheduler of a null_blk disk 20 times takes (median):
> 
>    operation             before (ms)  after (ms)  change
>    none -> none                13.09        9.06    -31%
>    mq-deadline -> none         11.99        7.96    -34%
> 
> Fixes: 734e1a8603128 ("block: Prevent deadlocks when switching elevators")
> Signed-off-by: Qiliang Yuan<qiliang.yuan@linux.dev>

Looks good to me:

Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>