From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96881C43460 for ; Fri, 16 Apr 2021 15:21:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 756D36101E for ; Fri, 16 Apr 2021 15:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343532AbhDPPVx (ORCPT ); Fri, 16 Apr 2021 11:21:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:41130 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343512AbhDPPUf (ORCPT ); Fri, 16 Apr 2021 11:20:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id EB32AAEF8; Fri, 16 Apr 2021 15:20:09 +0000 (UTC) To: Mike Snitzer Cc: Christoph Hellwig , Jens Axboe , dm-devel@redhat.com, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Chao Leng References: <20210415231530.95464-1-snitzer@redhat.com> <20210415231530.95464-3-snitzer@redhat.com> <20210416145340.GB16047@redhat.com> From: Hannes Reinecke Organization: SUSE Linux GmbH Subject: Re: [PATCH v2 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set Message-ID: <3c5d6257-5f49-877e-91c2-c6d7687b002b@suse.de> Date: Fri, 16 Apr 2021 17:20:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210416145340.GB16047@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 4/16/21 4:53 PM, Mike Snitzer wrote: > On Fri, Apr 16 2021 at 10:01am -0400, > Hannes Reinecke wrote: > >> On 4/16/21 1:15 AM, Mike Snitzer wrote: >>> From: Chao Leng >>> >>> REQ_FAILFAST_TRANSPORT was designed for SCSI, because the SCSI protocol >>> does not define the local retry mechanism. SCSI implements a fuzzy >>> local retry mechanism, so REQ_FAILFAST_TRANSPORT is needed to allow >>> higher-level multipathing software to perform failover/retry. >>> >>> NVMe is different with SCSI about this. It defines a local retry >>> mechanism and path error codes, so NVMe should retry local for non >>> path error. If path related error, whether to retry and how to retry >>> is still determined by higher-level multipathing's failover. >>> >>> Unlike SCSI, NVMe shouldn't prevent retry if REQ_FAILFAST_TRANSPORT >>> because NVMe's local retry is needed -- as is NVMe specific logic to >>> categorize whether an error is path related. >>> >>> In this way, the mechanism of NVMe multipath or other multipath are >>> now equivalent. The mechanism is: non path related error will be >>> retried locally, path related error is handled by multipath. >>> >>> Signed-off-by: Chao Leng >>> [snitzer: edited header for grammar and clarity, also added code comment] >>> Signed-off-by: Mike Snitzer >>> --- >>> drivers/nvme/host/core.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c >>> index 540d6fd8ffef..4134cf3c7e48 100644 >>> --- a/drivers/nvme/host/core.c >>> +++ b/drivers/nvme/host/core.c >>> @@ -306,7 +306,14 @@ static inline enum nvme_disposition nvme_decide_disposition(struct request *req) >>> if (likely(nvme_req(req)->status == 0)) >>> return COMPLETE; >>> >>> - if (blk_noretry_request(req) || >>> + /* >>> + * REQ_FAILFAST_TRANSPORT is set by upper layer software that >>> + * handles multipathing. Unlike SCSI, NVMe's error handling was >>> + * specifically designed to handle local retry for non-path errors. >>> + * As such, allow NVMe's local retry mechanism to be used for >>> + * requests marked with REQ_FAILFAST_TRANSPORT. >>> + */ >>> + if ((req->cmd_flags & (REQ_FAILFAST_DEV | REQ_FAILFAST_DRIVER)) || >>> (nvme_req(req)->status & NVME_SC_DNR) || >>> nvme_req(req)->retries >= nvme_max_retries) >>> return COMPLETE; >>> >> Huh? >> >> #define blk_noretry_request(rq) \ >> ((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \ >> REQ_FAILFAST_DRIVER)) >> >> making the only _actual_ change in your patch _not_ evaluating the >> REQ_FAILFAST_DRIVER, which incidentally is only used by the NVMe core. > > No, not sure how you got there. I'd have thought the 5 references to > "REQ_FAILFAST_TRANSPORT" would've been sufficient ;) > Ah. Misread stuff. You're excluding the REQ_FAILFAST_TRANSPORT here. But then it's _actually_ similar to the next patch (which I've also commented). Wouldn't it be better to fold them into one patch and discuss things together; especially as my comment to the next one might actually achieve the same thing? Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg)