Question about cmd_queue

["Kiwoong Kim" <kwmad.kim@samsung.com>]

> ufs_bsg was introduced nearly three years ago and it allocates its own
> request queue.

This is not related with ufs_bsg. I want to talk about a member under ufs_hba, cmd_queue.
Very sorry for making you confused.

> I faced a sytmpom with this and want to ask something about it.
> 
> That is, sometimes queue depth for ufs is limited to half of the its
> maximum value even in a situation with many IO requests from filesystem.
> It turned out that it only occurs when a query is being processed at the
> same time.
> Regarding my tracing, when the query process starts, users for the hctx
> that represents a ufs host increase to two and with this, some pathes
> calling 'hctx_may_queue'
> function in blk-mq seems to throttle dispatches, technically with 16
> because the number of ufs slots (32 in my case) is dividend by two (users).
> 
> I found that it happened when a query for write booster is processed
> because write booster only turns on in some conditions in my base that is
> different from kernel mainline. But when an exceptional event or others
> that could lead to a query occurs, it can happen even in mainline.
> 
> I think the throttling is a little bit excessive, so the question: is
> there any way to assign queue depth per user on an asymmetric basis?
> 
> Thanks.
> Kiwoong Kim