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[5.186.124.214]) by smtp.gmail.com with ESMTPSA id b17sm13218700eju.76.2020.12.07.11.24.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Dec 2020 11:24:54 -0800 (PST) From: "Javier =?utf-8?B?R29uesOhbGV6?=" X-Google-Original-From: Javier =?utf-8?B?R29uesOhbGV6?= Date: Mon, 7 Dec 2020 20:24:53 +0100 To: Hannes Reinecke Cc: Christoph Hellwig , SelvaKumar S , linux-nvme@lists.infradead.org, kbusch@kernel.org, axboe@kernel.dk, damien.lemoal@wdc.com, sagi@grimberg.me, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, snitzer@redhat.com, selvajove@gmail.com, nj.shetty@samsung.com, joshi.k@samsung.com, "Martin K. Petersen" , Bart Van Assche , Mikulas Patocka , linux-scsi@vger.kernel.org Subject: Re: [RFC PATCH v2 0/2] add simple copy support Message-ID: <20201207192453.vc6clbdhz73hzs7l@mpHalley> References: <20201204094659.12732-1-selvakuma.s1@samsung.com> <20201207141123.GC31159@lst.de> <01fe46ac-16a5-d4db-f23d-07a03d3935f3@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline In-Reply-To: <01fe46ac-16a5-d4db-f23d-07a03d3935f3@suse.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.12.2020 15:56, Hannes Reinecke wrote: >On 12/7/20 3:11 PM, Christoph Hellwig wrote: >>So, I'm really worried about: >> >> a) a good use case. GC in f2fs or btrfs seem like good use cases, as >> does accelating dm-kcopyd. I agree with Damien that lifting dm-kcopyd >> to common code would also be really nice. I'm not 100% sure it should >> be a requirement, but it sure would be nice to have >> I don't think just adding an ioctl is enough of a use case for complex >> kernel infrastructure. >> b) We had a bunch of different attempts at SCSI XCOPY support form IIRC >> Martin, Bart and Mikulas. I think we need to pull them into this >> discussion, and make sure whatever we do covers the SCSI needs. >> >And we shouldn't forget that the main issue which killed all previous >implementations was a missing QoS guarantee. >It's nice to have simply copy, but if the implementation is _slower_ >than doing it by hand from the OS there is very little point in even >attempting to do so. >I can't see any provisions for that in the TPAR, leading me to the >assumption that NVMe simple copy will suffer from the same issue. > >So if we can't address this I guess this attempt will fail, too. Good point. We can share some performance data on how Simple Copy scales in terms of bw / latency and the CPU usage. Do you have anything else in mind?