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=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,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 63360C433B4 for ; Fri, 16 Apr 2021 15:33:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4764F611ED for ; Fri, 16 Apr 2021 15:33:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343641AbhDPPdf (ORCPT ); Fri, 16 Apr 2021 11:33:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42463 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234887AbhDPPde (ORCPT ); Fri, 16 Apr 2021 11:33:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618587189; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Vqoh0bpBWbXkcp8vTRZHwAUESy3cKGws450KVMTeFV0=; b=IX2L5JETdXeGtNsoZdmisPz5TJa+/DWwz56GKJDE06OvEIOgaXc6yxJ6Dm5CAjkdQTTalW yHXAdkqhgA0VwiTLLEuV0Sh/Urr3FuS8VIKgJJ9P7yA2dwOsh9x6DkwTVV15C+ZgwYsCLn s6eZcDRrsUyS1SXkB1vUJUL8AQtPids= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-163-uf6B3rjCOcOC8At4J4euBA-1; Fri, 16 Apr 2021 11:33:05 -0400 X-MC-Unique: uf6B3rjCOcOC8At4J4euBA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0B6DF107ACC7; Fri, 16 Apr 2021 15:33:04 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3B9D25D749; Fri, 16 Apr 2021 15:33:00 +0000 (UTC) Date: Fri, 16 Apr 2021 11:32:59 -0400 From: Mike Snitzer To: Hannes Reinecke Cc: Christoph Hellwig , Jens Axboe , dm-devel@redhat.com, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Chao Leng Subject: Re: [PATCH v2 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set Message-ID: <20210416153259.GA20150@redhat.com> References: <20210415231530.95464-1-snitzer@redhat.com> <20210415231530.95464-3-snitzer@redhat.com> <20210416145340.GB16047@redhat.com> <3c5d6257-5f49-877e-91c2-c6d7687b002b@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3c5d6257-5f49-877e-91c2-c6d7687b002b@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Apr 16 2021 at 11:20am -0400, Hannes Reinecke wrote: > 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? 2 discrete things. This patch enables local retry. Patch 3 allows proper failover via upper layer multipathing. And as I replied, your suggestion about using DNR doesn't achieve the same thing (said as much in reply to the patch 3 thread). Mike