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Date:   Sun, 2 Apr 2023 19:24:17 -0600
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Subject: Re: [PATCH V6 00/17] io_uring/ublk: add generic IORING_OP_FUSED_CMD
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To:     Ming Lei <ming.lei@redhat.com>, io-uring@vger.kernel.org,
        linux-block@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, Miklos Szeredi <mszeredi@redhat.com>,
        ZiyangZhang <ZiyangZhang@linux.alibaba.com>,
        Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
        Bernd Schubert <bschubert@ddn.com>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>
References: <20230330113630.1388860-1-ming.lei@redhat.com>
 <ZConr0f8e/mEL0Cl@ovpn-8-18.pek2.redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <ZConr0f8e/mEL0Cl@ovpn-8-18.pek2.redhat.com>
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Precedence: bulk

On 4/2/23 7:11?PM, Ming Lei wrote:
> On Thu, Mar 30, 2023 at 07:36:13PM +0800, Ming Lei wrote:
>> Hello Jens and Guys,
>>
>> Add generic fused command, which can include one primary command and multiple
>> secondary requests. This command provides one safe way to share resource between
>> primary command and secondary requests, and primary command is always
>> completed after all secondary requests are done, and resource lifetime
>> is bound with primary command.
>>
>> With this way, it is easy to support zero copy for ublk/fuse device, and
>> there could be more potential use cases, such as offloading complicated logic
>> into userspace, or decouple kernel subsystems.
>>
>> Follows ublksrv code, which implements zero copy for loop, nbd and
>> qcow2 targets with fused command:
>>
>> https://github.com/ming1/ubdsrv/tree/fused-cmd-zc-for-v6
>>
>> All three(loop, nbd and qcow2) ublk targets have supported zero copy by passing:
>>
>> 	ublk add -t [loop|nbd|qcow2] -z .... 
>>
>> Also add liburing test case for covering fused command based on miniublk
>> of blktest.
>>
>> https://github.com/ming1/liburing/tree/fused_cmd_miniublk_for_v6
>>
>> Performance improvement is obvious on memory bandwidth related workloads,
>> such as, 1~2X improvement on 64K/512K BS IO test on loop with ramfs backing file.
>> ublk-null shows 5X IOPS improvement on big BS test when the copy is avoided.
>>
>> Please review and consider for v6.4.
>>
>> V6:
>> 	- re-design fused command, and make it more generic, moving sharing buffer
>> 	as one plugin of fused command, so in future we can implement more plugins
>> 	- document potential other use cases of fused command
>> 	- drop support for builtin secondary sqe in SQE128, so all secondary
>> 	  requests has standalone SQE
>> 	- make fused command as one feature
>> 	- cleanup & improve naming
> 
> Hi Jens,
> 
> Can you apply ublk cleanup patches 7~11 on for-6.4? For others, we may
> delay to 6.5, and I am looking at other approach too.

Done - and yes, we're probably looking at 6.5 for the rest. But that's
fine, I'd rather end up with the right interface than try and rush one.

-- 
Jens Axboe