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([2620:15c:211:201:5051:6ed0:9022:37aa]) by smtp.gmail.com with ESMTPSA id e15-20020a170902784f00b00196048cc113sm1877003pln.126.2023.01.27.16.47.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Jan 2023 16:47:44 -0800 (PST) Message-ID: Date: Fri, 27 Jan 2023 16:47:42 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v3 01/18] block: introduce duration-limits priority class Content-Language: en-US To: Damien Le Moal , Niklas Cassel Cc: Paolo Valente , Jens Axboe , Christoph Hellwig , Hannes Reinecke , "linux-scsi@vger.kernel.org" , "linux-ide@vger.kernel.org" , "linux-block@vger.kernel.org" References: <20230124190308.127318-2-niklas.cassel@wdc.com> <731aeacc-74c0-396b-efa0-f9ae950566d8@opensource.wdc.com> <873e0213-94b5-0d81-a8aa-4671241e198c@acm.org> <4c345d8b-7efa-85c9-fe1c-1124ea5d9de6@opensource.wdc.com> <5066441f-e265-ed64-fa39-f77a931ab998@acm.org> <275993f1-f9e8-e7a8-e901-2f7d3a6bb501@opensource.wdc.com> <86de1e78-0ff2-be70-f592-673bce76e5ac@opensource.wdc.com> <7f0a2464-673a-f64a-4ebb-e599c3123a24@acm.org> <29b50dbd-76e9-cdce-4227-a22223850c9a@opensource.wdc.com> <049a7e88-89d1-804f-a0b5-9e5d93d505f7@opensource.wdc.com> From: Bart Van Assche In-Reply-To: <049a7e88-89d1-804f-a0b5-9e5d93d505f7@opensource.wdc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-ide@vger.kernel.org On 1/27/23 16:40, Damien Le Moal wrote: > On 1/28/23 02:23, Bart Van Assche wrote: >> I hope that I have it made it clear that I think that the proposed user >> space API will be very painful to use for application developers. > > I completely disagree. Reusing the prio class/level API made it easy to allow > applications to use the feature. fio support for CDL requires exactly *one line* > change, to allow for the CDL class number 4. That's it. From there, one can use > the --cmdprio_class=4 nd --cmdprio=idx options to exercise a drive. The value of > "idx" here of course depends on how the descriptors are set on the drive. But > back to the point above. This depends on the application goals and the > descriptors are set accordingly for that goal. There is no real discovery needed > by the application. The application expect a certain set of CDL limits for its > use case, and checking that this set is the one currently defined on the drive > is easy to do from an application with the sysfs interface we added. > > Many users out there have deployed and using applications taking advantage of > ATA NCQ priority feature, using class RT for high priority IOs. The new CDL > class does not require many application changes to be enabled for next gen > drives that will have CDL. As I mentioned before, the new I/O priority class IOPRIO_CLASS_DL makes it impossible to use a single I/O priority class across devices that support CDL and devices that do not support CDL. I'm surprised that you keep denying that IOPRIO_CLASS_DL is a royal pain for users who have to support devices that support CDL and devices that do not support CDL. Bart.