linux-kernel - Question about cmd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <000001d7a92e$f4688800$dd399800$@samsung.com>
Date:   Tue, 14 Sep 2021 15:08:36 +0900
From:   "Kiwoong Kim" <kwmad.kim@...sung.com>
To:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <alim.akhtar@...sung.com>, <avri.altman@....com>,
        <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <beanhuo@...ron.com>, <cang@...eaurora.org>,
        <adrian.hunter@...el.com>, <sc.suh@...sung.com>,
        <hy50.seo@...sung.com>, <sh425.lee@...sung.com>,
        <bhoon95.kim@...sung.com>
Subject: Question about cmd_queue

> 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