linux-kernel - Re: [PATCH] block: BFQ default for single queue devices

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

Date:   Fri, 5 Oct 2018 20:12:27 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jan Kara <jack@...e.cz>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-mtd@...ts.infradead.org, Pavel Machek <pavel@....cz>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Richard Weinberger <richard@....at>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andreas Herrmann <aherrmann@...e.com>,
        Mel Gorman <mgorman@...e.com>,
        Chunyan Zhang <zhang.chunyan@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: BFQ default for single queue devices

On 10/5/18 2:16 AM, Jan Kara wrote:
> On Thu 04-10-18 15:42:52, Bart Van Assche wrote:
>> What I think is missing is measurement results for BFQ on a system with
>> multiple CPU sockets and against a fast storage medium. Eliminating
>> the host lock from the SCSI core yielded a significant performance
>> improvement for such storage devices. Since the BFQ scheduler locks and
>> unlocks bfqd->lock for every dispatch operation it is very likely that BFQ
>> will slow down I/O for fast storage devices, even if their driver only
>> creates a single hardware queue.
> 
> Well, I'm not sure why that is missing. I don't think anyone proposed to
> default to BFQ for such setup? Neither was anyone claiming that BFQ is
> better in such situation... The proposal has been: Default to BFQ for slow
> storage, leave it to deadline-mq otherwise.

Hi Jan,

How do you define slow storage? The proposal at the start of this thread 
was to make BFQ the default for all block devices that create a single 
hardware queue. That includes all SATA storage since scsi-mq only 
creates a single hardware queue when using the SATA protocol. The 
proposal to make BFQ the default for systems with a single hard disk 
probably makes sense but I am not sure that making BFQ the default for 
systems equipped with one or more (SATA) SSDs is also a good idea. 
Especially for multi-socket systems since BFQ reintroduces a queue-wide 
lock. As you know no queue-wide locking happens during I/O in the 
scsi-mq core nor in the blk-mq core.

Bart.