linux-kernel - Re: [WIP PATCHSET 0/4] WIP branch for bfq-mq

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Date:   Mon, 13 Feb 2017 22:07:12 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Bart Van Assche <bart.vanassche@...disk.com>
Cc:     "tj@...nel.org" <tj@...nel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>
Subject: Re: [WIP PATCHSET 0/4] WIP branch for bfq-mq


> Il giorno 10 feb 2017, alle ore 20:49, Paolo Valente <paolo.valente@...aro.org> ha scritto:
> 
>> 
>> Il giorno 10 feb 2017, alle ore 19:13, Bart Van Assche <bart.vanassche@...disk.com> ha scritto:
>> 
>> On 02/10/2017 08:49 AM, Paolo Valente wrote:
>>>> $ grep '^C.*_MQ_' .config
>>>> CONFIG_BLK_MQ_PCI=y
>>>> CONFIG_MQ_IOSCHED_BFQ=y
>>>> CONFIG_MQ_IOSCHED_DEADLINE=y
>>>> CONFIG_MQ_IOSCHED_NONE=y
>>>> CONFIG_DEFAULT_MQ_BFQ_MQ=y
>>>> CONFIG_DEFAULT_MQ_IOSCHED="bfq-mq"
>>>> CONFIG_SCSI_MQ_DEFAULT=y
>>>> CONFIG_DM_MQ_DEFAULT=y
>>>> 
>>> 
>>> Could you reconfigure with none or mq-deadline as default, check
>>> whether the system boots, and, it it does, switch manually to bfq-mq,
>>> check what happens, and, in the likely case of a failure, try to get
>>> the oops?
>> 
>> Hello Paolo,
>> 
>> I just finished performing that test with the following kernel config:
>> $ grep '^C.*_MQ_' .config
>> CONFIG_BLK_MQ_PCI=y
>> CONFIG_MQ_IOSCHED_BFQ=y
>> CONFIG_MQ_IOSCHED_DEADLINE=y
>> CONFIG_MQ_IOSCHED_NONE=y
>> CONFIG_DEFAULT_MQ_DEADLINE=y
>> CONFIG_DEFAULT_MQ_IOSCHED="mq-deadline"
>> CONFIG_SCSI_MQ_DEFAULT=y
>> CONFIG_DM_MQ_DEFAULT=y
>> 
>> After the system came up I logged in, switched to the bfq-mq scheduler
>> and ran several I/O tests against the boot disk.
> 
> Without any failure, right?
> 
> Unfortunately, as you can imagine, no boot failure occurred on
> any of my test systems so far :(
> 
> This version of bfq-mq can be configured to print all its activity in
> the kernel log, by just defining a macro.  This will of course slow
> down the system so much to make it probably unusable, if bfq-mq is
> active from boot.  Yet, the failure may still occur so early to make
> this approach useful to discover where bfq-mq gets stuck.  As of now I
> have no better ideas.  Any suggestion is welcome.
> 

Hi Bart,
I have found a machine crashing at boot, yet not only when bfq-mq is
chosen, but also when mq-deadline is chosen as the default
scheduler.  I have found and just reported the cause of the failure,
together with a fix.  Probably this is not the cause of your failure,
but what do you think about trying this fix?  BTW, I have rebased the
branch [1] against the new commits in Jens for-4.11/next.

Otherwise, if you have no news or suggestions, would you be willing to
try my micro-logging proposal?

Thanks,
Paolo

[1] https://github.com/Algodev-github/bfq-mq

> Thanks,
> Paolo
> 
>> Sorry but nothing
>> interesting appeared in the kernel log.
>> 
>> Bart.
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