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Subject: Re: Spurious instability with NFSoRDMA under moderate load
From:   Timo Rothenpieler <timo@rothenpieler.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Olga Kornievskaia <aglo@umich.edu>,
        Dai Ngo <dai.ngo@oracle.com>
References: <4da3b074-a6be-d83f-ccd4-b151557066aa@rothenpieler.org>
 <e12c24fd-beaf-31ce-cb49-36ad32bd22b3@rothenpieler.org>
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 <9355de20-921c-69e0-e5a4-733b64e125e1@rothenpieler.org>
 <a28b403e-42cf-3189-a4db-86d20da1b7aa@rothenpieler.org>
 <4BA2A532-9063-4893-AF53-E1DAB06095CC@oracle.com>
 <c8025457-7376-e1b7-bd6c-e5c6ee5d9ce7@rothenpieler.org>
 <141fdf51-2aa1-6614-fe4e-96f168cbe6cf@rothenpieler.org>
 <99DFF0B0-FE0F-4416-B3F6-1F9535884F39@oracle.com>
 <64F9A492-44B9-4057-ABA5-C8202828A8DD@oracle.com>
 <1b8a24a9-5dba-3faf-8b0a-16e728a6051c@rothenpieler.org>
 <5DD80ADC-0A4B-4D95-8CF7-29096439DE9D@oracle.com>
 <0444ca5c-e8b6-1d80-d8a5-8469daa74970@rothenpieler.org>
 <cc2f55cd-57d4-d7c3-ed83-8b81ea60d821@rothenpieler.org>
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 <7B44D7FD-9D0F-4A0D-ABE9-E295072D953F@oracle.com>
 <97fe445e-6c4f-b7cf-fa39-fd0c4222a89e@rothenpieler.org>
Message-ID: <c3e31e57-15fa-8f70-bbb8-af5452c1f5fc@rothenpieler.org>
Date:   Wed, 18 Aug 2021 02:03:16 +0200
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On 17.08.2021 23:51, Timo Rothenpieler wrote:
> On 17.08.2021 23:08, Chuck Lever III wrote:
>> I tried reproducing this using your 'xfs_io -fc "copy_range
>> testfile" testfile.copy' reproducer, but couldn't.
>>
>> A network capture shows that the client tries CLONE first. The
>> server reports that's not supported, so the client tries COPY.
>> The COPY works, and the reply shows that the COPY was synchro-
>> nous. Thus there's no need for a callback, and I'm not tripping
>> over backchannel misbehavior.
>=20
> Make sure the testfile is of sufficient size. I'm not sure what the=20
> threshold is, but if it's too small, it'll just do a synchronous copy=20
> for me as well.
> I'm using a 50MB file in my tests.
>=20
>> The export I'm using is an xfs filesystem. Did you already
>> report the filesystem type you're testing against? I can't
>> find it in the thread.
>>
>> If there's a way to force an offload-style COPY, let me know.
>>
>> Oh. Also I looked at what might have been pulled into the
>> linux-5.12.y kernel between .12 and .19, and I don't see
>> anything that's especially relevant to either COPY_OFFLOAD
>> or backchannel.
>=20
> I'm observing this with both an ext4 and zfs filesystem.
> Can easily test xfs as well if desired.

Re-ran the test with xfs instead of ext4, and indeed, the issue does not =

manifest in that case.
I guess xfs is lacking some capability for server side copy to work=20
properly.

> Are you testing this on a normal network, or with RDMA? With normal tcp=
,=20
> I also can't observe this issue(it doesn't time out the backchannel in =

> the first place), it only happens in RDMA mode.
> I'm using Mellanox ConnectX-4 cards in IB mode for my tests.
>=20


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