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Subject: Re: [PATCH IMPROVEMENT] block, bfq: limit sectors served with
 interactive weight raising
From: Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <c1cb979a-007c-7607-0c02-4f9110f90a13@applied-asynchrony.com>
Date: Fri, 12 Jan 2018 11:20:44 +0100
Cc: Jens Axboe <axboe@kernel.dk>,
        linux-block <linux-block@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Mark Brown <broonie@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        bfq-iosched@googlegroups.com, oleksandr@natalenko.name
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Message-Id: <9F56E963-E99C-4B7A-B66A-83FC29B544CD@linaro.org>
References: <20171228111917.2767-1-paolo.valente@linaro.org>
 <5a9c6573-84a6-ae7b-7058-f202c7187065@applied-asynchrony.com>
 <12660CC7-AD89-434A-9BEA-BA0B4C362807@linaro.org>
 <c1cb979a-007c-7607-0c02-4f9110f90a13@applied-asynchrony.com>
To: =?utf-8?Q?Holger_Hoffst=C3=A4tte?= <holger@applied-asynchrony.com>
Sender: linux-kernel-owner@vger.kernel.org


> Il giorno 12 gen 2018, alle ore 11:15, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto:
> 
> On 01/12/18 06:58, Paolo Valente wrote:
>> 
>> 
>>> Il giorno 28 dic 2017, alle ore 15:00, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto:
>>> 
>>> 
>>> On 12/28/17 12:19, Paolo Valente wrote:
>>> (snip half a tech report ;)
>>> 
>>> So either this or the previous patch ("limit tags for writes and async I/O"
>>> can lead to a hard, unrecoverable hang with heavy writes. Since I couldn't
>>> log into the affected system anymore I couldn't get any stack traces, blk-mq
>>> debug output etc. but there was nothing in dmesg/on the console, so it
>>> wasn't a BUG/OOPS.
>>> 
>>> -h
>> 
>> Hi Holger,
>> if, as I guess, this problem hasn't gone away for you, I have two
>> requests:
>> 1) could you share your exact test
>> 2) if nothing happens in my systems with your test, would you be
>> willing to retry with the dev version of bfq?  It should be able to
>> tell us what takes to your hang.  If you are willing to do this test,
>> I'll prepare a branch with everything already configured for you.
> 
> Hi,
> 
> thanks for following up but there's no need for any of that; it turned out
> to be something else since I got the same hang without those patches at
> least once (during a btrfs balance, even though it didn't look like btrfs'
> fault directly; more like block/mm/helpers.
> 
> So on January 7 I posted to linux-block et.al. where I said
> "So this turned out to be something else, sorry for the false alarm."
> but apparently that didn't make it through since it's not in the
> archives either. Sorry.
> 
> Long story short, the good news is that I've been running with both patches
> since then without any issue. :)
> 

Wow, what a relief! :)

So, Jens, being the only issue reported gone, can you please consider
queueing this patch and the other pending one [1]?  They are both
critical for bfq performance.

Thanks,
Paolo

[1] https://www.spinics.net/lists/kernel/msg2684463.html

> cheers
> Holger