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Mon, 10 Mar 2025 16:44:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id MOEIFd8Wz2fPYwAAD6G6ig (envelope-from ); Mon, 10 Mar 2025 16:44:15 +0000 Message-ID: <84a87c16-0738-460d-b83f-55f8181d536e@suse.de> Date: Mon, 10 Mar 2025 17:44:14 +0100 Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] [v2]aacraid: Reply queue mapping to CPUs based on IRQ affinity To: John Meneghini , "Martin K. Petersen" , pheidologeton@protonmail.com, kernel@roadkil.net, maokaman@gmail.com Cc: Sagar.Biradar@microchip.com, "James E.J. Bottomley" , linux-scsi@vger.kernel.org, thenzl@redhat.com, mpatalan@redhat.com, Scott.Benesh@microchip.com, Don.Brace@microchip.com, Tom.White@microchip.com, Abhinav.Kuchibhotla@microchip.com References: <20250130173314.608836-1-sagar.biradar@microchip.com> <8433b8b8-bb9a-43e0-a760-d8745d28d0d9@redhat.com> <2eca14e0-3978-440f-a4a4-32c9c61baad4@redhat.com> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <2eca14e0-3978-440f-a4a4-32c9c61baad4@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FREEMAIL_TO(0.00)[redhat.com,oracle.com,protonmail.com,roadkil.net,gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com,protonmail.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email] X-Spam-Flag: NO X-Spam-Level: On 2/24/25 22:15, John Meneghini wrote: > On 2/20/25 9:38 PM, Martin K. Petersen wrote: >> >> John, >> >>> However, I agree it would be better to just fix the driver, >>> performance impact notwithstanding, and ship it. For my part I'd >>> rather have a correctly functioning driver, that's slower, but doesn't >>> panic. >> >> I prefer to have a driver that doesn't panic when the user performs a >> reasonably normal administrative action. > > Agreed. The only clarification I want to make is that users will > not see a panic, they will see IO timeouts and Host bus resets. > It was my mistake to report earlier that the host would panic. > > When aac_cpu_offline_feature is disabled users will see higher performance > but if they start off-lining CPUS they may see IO timeouts.  This is the > state of the current driver and this is the problem which the original > patch: > commit 9dc704dcc09e ("scsi: aacraid: Reply queue mapping to CPUs based > on IRQ affinity") > was supposed to have fixed. The problem was the original patch didn't > fix the > problem correctly and it resulted in the regression reported in Bugzilla > 217599[1]. > > This patch circles back and fixes the original problem correctly. The extra > 'aac_cpu_offline_feature' modparam was added to disable the new code path > because of concerns raised during our testing at Red Hat about reduced > performance with this patch. > >> If go-faster stripes are desired in specific configurations, then make >> the performance mode an opt-in. Based on your benchmarks, however, I'm >> not entirely convinced it's worth it... > > I agree.  So how about if we can just take out the > aac_cpu_offline_feature modparam...? > > Alternatively we can replace the modparam with a kConfig option. The > default setting for the new Kconfig option will be offline_cpu_support_on and > performance_mode_off. That way we can ship a default kernel configuration that > provides a working aacraid driver which safely supports off-lining > CPUS. If people are really unhappy with the performance, and they> don't care about offline cpu support, they can re-config their kernel. > > Personally I prefer option 1, but we the thoughts of the upstream users. > > I've added the original authors of Bugzilla 217599[1] to the cc list to > get their attention and review. > Do we have an idea what these 'specific use-cases' are? And how much performance impact we have? I could imagine a single-threaded workload driving just one blk-mq queue would benefit from spreading out onto several interrupts. But then, this would be true for most of the multiqueue drivers; and indeed quite some drivers (eg megaraid_sas & mpt3sas 'smp_affinity_enable') have the very same module option. Wouldn't it be an idea to check if we can make this a generic / blk-mq queue option instead of having each driver to implement the same functionality on it's own? Topic for LSF? 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