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([2620:10d:c092:600::1:d656]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4831089d547sm52311635e9.14.2026.02.04.03.38.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Feb 2026 03:38:10 -0800 (PST) Message-ID: <82f0e957-94ef-45d6-971b-951540bce136@gmail.com> Date: Wed, 4 Feb 2026 11:38:09 +0000 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] dmabuf backed read/write To: Keith Busch Cc: linux-block@vger.kernel.org, io-uring , "linux-nvme@lists.infradead.org" , "Gohad, Tushar" , =?UTF-8?Q?Christian_K=C3=B6nig?= , Christoph Hellwig , Kanchan Joshi , Anuj Gupta , Nitesh Shetty , "lsf-pc@lists.linux-foundation.org" References: <4796d2f7-5300-4884-bd2e-3fcc7fdd7cea@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/3/26 18:07, Keith Busch wrote: > On Tue, Feb 03, 2026 at 02:29:55PM +0000, Pavel Begunkov wrote: >> Good day everyone, >> ... >> Tushar was helping and mention he got good numbers for P2P transfers >> compared to bouncing it via RAM. Anuj, Kanchan and Nitesh also >> previously reported encouraging results for system memory backed >> dma-buf for optimising IOMMU overhead, quoting Anuj: >> >> - STRICT: before = 570 KIOPS, after = 5.01 MIOPS >> - LAZY: before = 1.93 MIOPS, after = 5.01 MIOPS >> - PASSTHROUGH: before = 5.01 MIOPS, after = 5.01 MIOPS > > Thanks for submitting the topic. The performance wins look great, but > I'm a little surpised passthrough didn't show any difference. We're > still skipping a bit of transformations with the dmabuf compared to not > having it, so maybe it's just a matter of crafting the right benchmark > to show the benefit. My first thought was that hardware couldn't push more and would be great to have idle numbers, but Anuj already demystified it. > Anyway, I look forward to the next version of this feature. I promise to > have more cycles to review and test the v3. Thanks! And in general, IMHO at this point waiting for next version would be more time efficient for reviewers. -- Pavel Begunkov