linux-ext4 - Re: mmc: block: bonnie++ runs with errors on arc/hsdk board

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]

Message-ID: <1521220236.10304.10.camel@synopsys.com>
Date:   Fri, 16 Mar 2018 17:10:37 +0000
From:   Evgeniy Didin <Evgeniy.Didin@...opsys.com>
To:     "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "Evgeniy.Didin@...opsys.com" <Evgeniy.Didin@...opsys.com>
CC:     "jh80.chung@...sung.com" <jh80.chung@...sung.com>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: mmc: block: bonnie++ runs with errors on arc/hsdk board

Hello Adrian,

> Yes.  Unfortunately the clock used is not accurate enough to correctly order
> the events across different CPUs, which makes it very hard to see delays
> between requests.  You could try a different clock - refer the --clockid
> option to perf record.
> 
> Nevertheless it shows there are no I/O errors which means the error recovery
> can be ruled out as a problem.
> 
> The issue could be caused by the I/O scheduler.  Under blk-mq the default
> scheduler is the mq-deadline scheduler whereas without blk-mq you would
> probably have been using cfq by default.  You could try the bfq scheduler:
> 
> 	echo bfq > /sys/block/mmcblk0/queue/scheduler
> 
> But you might need to add it to the kernel config i.e.
> 
> 	CONFIG_IOSCHED_BFQ=y
> 
Switching from mq-deadline scheduler to bfq fixed the issue.
Also bonnie++ results have changed:
-----------------------------------------------<8----------------------------------------------------------------------------
bfq scheduler:
ARCLinux,512M,6463,87,7297,0,5450,0,9827,99,342952,99,+++++,+++,16,17525,100,+++++,+++,24329,99,17621,100,+++++,+++,24001,101

mq-deadline scheduler:
ARCLinux,512M,4453,36,6474,1,5852,0,12940,99,344329,100,+++++,+++,16,22168,98,+++++,+++,32760,99,22755,100,+++++,+++,32205,100
-----------------------------------------------<8----------------------------------------------------------------------------
As I see, the performance of sequential input per char and of file operations have decreased for ~25%.

Do you have any idea what could be a reason for such a long stalling in case of mq-deadline IOscheduler? I would expect if there is 
some long async operation, kernel should not be blocked. But what we see using mq-deadline is kernel blocked in bit_wait_io().
Do you think this is a valid behavior at least in case of mq-deadline IOscheduler?

> Alternatively you could fiddle with the scheduler parameters:
> 
> With mq-deadline they are:
> 
> # grep -H . /sys/block/mmcblk0/queue/iosched/*
> /sys/block/mmcblk0/queue/iosched/fifo_batch:16
> /sys/block/mmcblk0/queue/iosched/front_merges:1
> /sys/block/mmcblk0/queue/iosched/read_expire:500
> /sys/block/mmcblk0/queue/iosched/write_expire:5000
> /sys/block/mmcblk0/queue/iosched/writes_starved:2
> 
> You could try decreasing the write_expire and/or fifo_batch.
It seems that decreasing doesn't affect on this issue.

Best regards,
Evgeniy Didin