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Fri, 05 Apr 2024 06:21:14 +0000 Message-ID: Date: Fri, 5 Apr 2024 08:21:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv2 0/2] block,nvme: latency-based I/O scheduler Content-Language: en-US To: Keith Busch , Hannes Reinecke Cc: Christoph Hellwig , Sagi Grimberg , Jens Axboe , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org References: <20240403141756.88233-1-hare@kernel.org> From: Hannes Reinecke In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.50 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:98:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap2.dmz-prg2.suse.org:helo,imap2.dmz-prg2.suse.org:rdns,suse.de:dkim,suse.de:email]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Action: no action X-Rspamd-Queue-Id: 4F98821A19 X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240404_232120_084972_1CFFDDF9 X-CRM114-Status: GOOD ( 11.74 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 4/4/24 23:14, Keith Busch wrote: > On Wed, Apr 03, 2024 at 04:17:54PM +0200, Hannes Reinecke wrote: >> Hi all, >> >> there had been several attempts to implement a latency-based I/O >> scheduler for native nvme multipath, all of which had its issues. >> >> So time to start afresh, this time using the QoS framework >> already present in the block layer. >> It consists of two parts: >> - a new 'blk-nlatency' QoS module, which is just a simple per-node >> latency tracker >> - a 'latency' nvme I/O policy > > Whatever happened with the io-depth based path selector? That should > naturally align with the lower latency path, and that metric is cheaper > to track. Turns out that tracking queue depth (on the NVMe level) always requires an atomic, and with that a performance impact. The qos/blk-stat framework is already present, and as the numbers show actually leads to a performance improvement. So I'm not quite sure what the argument 'cheaper to track' buys us here... Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich