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[66.183.142.209]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35fb14f86d7sm2768181a91.4.2026.04.13.20.21.13 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Apr 2026 20:21:14 -0700 (PDT) From: "Doug Smythies" To: Cc: "'Nilay Shroff'" , "'Bart Van Assche'" , "'Jens Axboe'" , , "Doug Smythies" References: <005201dcc7ae$54a33010$fde99030$@telus.net> <9c1424f1-5d81-4308-bc93-0bdcde788501@fnnas.com> <004b01dcc8a9$7d6ac610$78405230$@telus.net> <6e336fc5-bf39-41eb-a499-6728969bf164@fnnas.com> In-Reply-To: <6e336fc5-bf39-41eb-a499-6728969bf164@fnnas.com> Subject: RE: REGRESSION BISECTED: mq-deadline: covert to use request_queue->async_depth Date: Mon, 13 Apr 2026 20:21:16 -0700 Message-ID: <002901dccbbd$c1c96110$455c2330$@telus.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-ca Thread-Index: AQGaHkQuMM6O6DZ6u71zkEMmWe5OhwJww55XAsViVaIAoA1gorY0iWJw Hi Kuai, Thank you for your replies, and the time you took to write them. On 2026.04.10 09:21 Yu Kuai wrote: > Hi, >=20 > =E5=9C=A8 2026/4/10 13:18, Doug Smythies =E5=86=99=E9=81=93: >>> Do you ever use the async_depth for mq-deadline? >> No. > > Then the only difference is the tag wake batch is changed from 1 to 8. = However, > batch wake up is the base design of sbitmap. And I do admit tail = latency is > bad under high concurrency is probably due to wake up is unfair, this = is a > know sbitmap design flaw and not fixed yet. Good to know. > You could try change wake up batch back to 1. However, I don't think = this is a > good solution. And I'll suggest you to try increase nr_requests to see = if tail > Latency gets better. I just observed what I thought was a pretty significant regression, and = thought I should bring it the attention of the stake holders. By decreasing the maximum concurrency of my workflow from 1000 to 64 the = regression decreased to noise levels, +/- 1.5%. Thanks, Doug Smythies