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Tue, 16 Jul 2024 06:37:48 +0000 Message-ID: Date: Tue, 16 Jul 2024 08:37:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] nvme_core: scan namespaces asynchronously Content-Language: en-US To: Stuart Hayes , linux-kernel@vger.kernel.org, Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , linux-nvme@lists.infradead.org Cc: Martin Wilck , Ayush Siddarath References: <20240715203434.20212-1-stuart.w.hayes@gmail.com> From: Hannes Reinecke In-Reply-To: <20240715203434.20212-1-stuart.w.hayes@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-2.79 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; FREEMAIL_TO(0.00)[gmail.com,vger.kernel.org,kernel.org,kernel.dk,lst.de,grimberg.me,lists.infradead.org]; TAGGED_RCPT(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email] X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240715_233755_126195_B82E8686 X-CRM114-Status: GOOD ( 38.35 ) 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 7/15/24 22:34, Stuart Hayes wrote: > Use async function calls to make namespace scanning happen in parallel. > > Without the patch, NVME namespaces are scanned serially, so it can take > a long time for all of a controller's namespaces to become available, > especially with a slower (TCP) interface with large number of > namespaces. > > It is not uncommon to have large numbers (hundreds or thousands) of > namespaces on nvme-of with storage servers. > > The time it took for all namespaces to show up after connecting (via > TCP) to a controller with 1002 namespaces was measured on one system: > > network latency without patch with patch > 0 6s 1s > 50ms 210s 10s > 100ms 417s 18s > > Measurements taken on another system show the effect of the patch on the > time nvme_scan_work() took to complete, when connecting to a linux > nvme-of target with varying numbers of namespaces, on a network of > 400us. > > namespaces without patch with patch > 1 16ms 14ms > 2 24ms 16ms > 4 49ms 22ms > 8 101ms 33ms > 16 207ms 56ms > 100 1.4s 0.6s > 1000 12.9s 2.0s > > On the same system, connecting to a local PCIe NVMe drive (a Samsung > PM1733) instead of a network target: > > namespaces without patch with patch > 1 13ms 12ms > 2 41ms 13ms > > Signed-off-by: Stuart Hayes > --- > changes from V2: > * make a separate function nvme_scan_ns_async() that calls > nvme_scan_ns(), instead of modifying nvme_scan_ns() > * only scan asynchronously from nvme_scan_ns_list(), not from > nvme_scan_ns_sequential() > * provide more timing data in the commit message > > changes from V1: > * remove module param to enable/disable async scanning > * add scan time measurements to commit message > > > drivers/nvme/host/core.c | 48 +++++++++++++++++++++++++++++++++------- > 1 file changed, 40 insertions(+), 8 deletions(-) > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c > index 782090ce0bc1..dbf05cfea063 100644 > --- a/drivers/nvme/host/core.c > +++ b/drivers/nvme/host/core.c > @@ -4,6 +4,7 @@ > * Copyright (c) 2011-2014, Intel Corporation. > */ > > +#include > #include > #include > #include > @@ -3952,6 +3953,30 @@ static void nvme_scan_ns(struct nvme_ctrl *ctrl, unsigned nsid) > } > } > > +/* > + * struct async_scan_info - keeps track of controller & NSIDs to scan > + * @ctrl: Controller on which namespaces are being scanned > + * @next_idx: Index of next NSID to scan in ns_list > + * @ns_list: Pointer to list of NSIDs to scan > + */ > +struct async_scan_info { > + struct nvme_ctrl *ctrl; > + atomic_t next_idx; > + __le32 *ns_list; > +}; > + > +static void nvme_scan_ns_async(void *data, async_cookie_t cookie) > +{ > + struct async_scan_info *scan_info = data; > + int idx; > + u32 nsid; > + > + idx = (u32)atomic_fetch_add(1, &scan_info->next_idx); > + nsid = le32_to_cpu(scan_info->ns_list[idx]); > + > + nvme_scan_ns(scan_info->ctrl, nsid); > +} > + > static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl, > unsigned nsid) > { > @@ -3975,12 +4000,14 @@ static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl, > static int nvme_scan_ns_list(struct nvme_ctrl *ctrl) > { > const int nr_entries = NVME_IDENTIFY_DATA_SIZE / sizeof(__le32); > - __le32 *ns_list; > + struct async_scan_info scan_info; > u32 prev = 0; > int ret = 0, i; > + ASYNC_DOMAIN(domain); > > - ns_list = kzalloc(NVME_IDENTIFY_DATA_SIZE, GFP_KERNEL); > - if (!ns_list) > + scan_info.ctrl = ctrl; > + scan_info.ns_list = kzalloc(NVME_IDENTIFY_DATA_SIZE, GFP_KERNEL); > + if (!scan_info.ns_list) > return -ENOMEM; > > for (;;) { > @@ -3990,28 +4017,33 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl) > .identify.nsid = cpu_to_le32(prev), > }; > > - ret = nvme_submit_sync_cmd(ctrl->admin_q, &cmd, ns_list, > - NVME_IDENTIFY_DATA_SIZE); > + ret = nvme_submit_sync_cmd(ctrl->admin_q, &cmd, > + scan_info.ns_list, > + NVME_IDENTIFY_DATA_SIZE); > if (ret) { > dev_warn(ctrl->device, > "Identify NS List failed (status=0x%x)\n", ret); > goto free; > } > > + atomic_set(&scan_info.next_idx, 0); > for (i = 0; i < nr_entries; i++) { > - u32 nsid = le32_to_cpu(ns_list[i]); > + u32 nsid = le32_to_cpu(scan_info.ns_list[i]); > > if (!nsid) /* end of the list? */ > goto out; > - nvme_scan_ns(ctrl, nsid); > + async_schedule_domain(nvme_scan_ns_async, &scan_info, > + &domain); > while (++prev < nsid) > nvme_ns_remove_by_nsid(ctrl, prev); > } > + async_synchronize_full_domain(&domain); Let me see if I get this right ... You allocate 'scan_info' on the stack, so every call to 'async_schedule_domain()' in the loop will be using the same scan_info context, right? So each instance of nvme_scan_ns_async() will be using whichever value is in 'next_idx', right? Effectively making 'nvme_scan_ns_async()' completely free-floating, spawning 'nr_entry' instances, and letting each instance pick whichever nsid is (at the time of execution) the next one. If that's the case then I would welcome some comments in the code, as this is somewhat non-obvious. And it also spells out clearly why the atomic 'next_idx' value is absolutely crucial to that mechanism, and we don't want anyone getting wrong ideas by 'optimizing' that away. Otherwise: Reviewed-by: Hannes Reinecke 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