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Re: [PATCH 0/2] block: add logging facility for long standing IO request

From: Denis V. Lunev
Subject: Re: [PATCH 0/2] block: add logging facility for long standing IO requests
Date: Fri, 31 Jul 2020 13:31:51 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 7/31/20 1:25 PM, Stefan Hajnoczi wrote:
> On Fri, Jul 10, 2020 at 08:27:09PM +0300, Denis V. Lunev wrote:
>> There are severe delays with IO requests processing if QEMU is running in
>> virtual machine or over software defined storage. Such delays potentially
>> results in unpredictable guest behavior. For example, guests over IDE or
>> SATA drive could remount filesystem read-only if write is performed
>> longer than 10 seconds.
>> Such reports are very complex to process. Some good starting point for this
>> seems quite reasonable. This patch provides one. It adds logging of such
>> potentially dangerous long IO operations.
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> CC: Max Reitz <mreitz@redhat.com>
> If I understand correctly this only reports completed I/Os, so if the
> host hasn't given up on an I/O request yet then QEMU will not report it
> is taking a long time. In the meantime the guest could start printing
> timeout errors.
> I think this patch series is good as it is. In the future maybe a QMP
> command that lists in-flight I/O requests would be nice. That helps
> when troubleshooting I/Os that are hung.
We could dump requests at block level, we do have proper lists,
but the would be a little bit different.

Anyway, I __DO__ like this idea, I have missed this somehow :)

Thank you for the suggestion,

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