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Subject: Re: stalling IO regression since linux 5.12, through 5.18
To:     Jan Kara <jack@suse.cz>, Chris Murphy <lists@colorremedies.com>
Cc:     Nikolay Borisov <nborisov@suse.com>, Jens Axboe <axboe@kernel.dk>,
        Paolo Valente <paolo.valente@linaro.org>,
        Linux-RAID <linux-raid@vger.kernel.org>,
        linux-block <linux-block@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Josef Bacik <josef@toxicpanda.com>
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From:   =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= <holger@applied-asynchrony.com>
Organization: Applied Asynchrony, Inc.
Message-ID: <902f766d-160a-f384-67d5-fa77c1d5caec@applied-asynchrony.com>
Date:   Wed, 17 Aug 2022 20:21:39 +0200
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On 2022-08-17 20:15, Jan Kara wrote:
> On Wed 17-08-22 13:57:00, Chris Murphy wrote:
>> On Wed, Aug 17, 2022, at 12:47 PM, Chris Murphy wrote:
>> Can you boot with
>>>> "megaraid_sas.host_tagset_enable = 0" kernel option and see whether the
>>>> issue reproduces?
>>
>> This has been running an hour without symptoms. It's strongly suggestive,
>> but needs to run overnight to be sure. Anecdotally, the max write IO is
>> less than what I'm used to seeing.
> 
> OK, if this indeed passes then b6e68ee82585 ("blk-mq: Improve performance
> of non-mq IO schedulers with multiple HW queues") might be what's causing
> issues (although I don't know how yet...).
> 
> 								Honza

Certainly explains why BFQ turned up as a suspect, considering it's still
single-queue (fair MQ scheduling is .. complicated).

-h