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Wed, 16 Apr 2025 06:39:10 -0700 (PDT) Date: Wed, 16 Apr 2025 06:39:09 -0700 From: Mohamed Khalfella To: Daniel Wagner Cc: Daniel Wagner , Christoph Hellwig , Sagi Grimberg , Keith Busch , Hannes Reinecke , John Meneghini , randyj@purestorage.com, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 3/3] nvme: delay failover by command quiesce timeout Message-ID: <20250416133909.GH1868505-mkhalfella@purestorage.com> References: <20250324-tp4129-v1-0-95a747b4c33b@kernel.org> <20250324-tp4129-v1-3-95a747b4c33b@kernel.org> <20250410085137.GE1868505-mkhalfella@purestorage.com> <6f0d50b2-7a16-4298-8129-c3a0b1426d26@flourine.local> <20250416001738.GA78596-mkhalfella@purestorage.com> <22e48664-63f3-4cc0-8b99-f56e98204e5b@flourine.local> 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=us-ascii Content-Disposition: inline In-Reply-To: <22e48664-63f3-4cc0-8b99-f56e98204e5b@flourine.local> On 2025-04-16 08:57:19 +0200, Daniel Wagner wrote: > On Tue, Apr 15, 2025 at 05:17:38PM -0700, Mohamed Khalfella wrote: > > Help me see this: > > > > - nvme_failover_req() is the only place reqs are added to failover_list. > > - nvme_decide_disposition() returns FAILOVER only if req has REQ_NVME_MPATH set. > > > > How/where do admin requests get REQ_NVME_MPATH set? > > Admin commands don't set REQ_NVME_MPATH. This is what the current code > does and I have deliberately decided not to touch this with this RFC. > > Given how much discussion the CQT/CCR feature triggers, I don't think > it's a good idea to add this topic to this discussion. > The point is that holding requests at nvme_failover_req() does not cover admin requests. Do you plan to add support for holding admin requests in the next revision of these patches? > > > > - What about requests that do not go through nvme_failover_req(), like > > > > passthrough requests, do we not want to hold these requests until it > > > > is safe for them to be retried? > > > > > > Pasthrough commands should fail immediately. Userland is in charge here, > > > not the kernel. At least this what should happen here. > > > > > > > - In case of controller reset or delete if nvme_disable_ctrl() > > > > successfully disables the controller, then we do not want to add > > > > canceled requests to failover_list, right? Does this implementation > > > > consider this case? > > > > > > Not sure. I've tested a few things but I am pretty sure this RFC is far > > > from being complete. > > > > I think it does not, and maybe it should honor this. Otherwise every > > controller reset/delete will end up holding requests unnecessarily. > > Yes, this is one of the problems with the failover queue. It could be > solved by really starting to track the delay timeout for each commands. > But this is a lot of logic code and complexity. Thus during the > discussion at LSFMM everyone including me, said failover queue idea > should not be our first choice. Got it. I assume this will be addressed in the next revision?