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Message-Id: <20240717185550.22102-1-stuart.w.hayes@gmail.com>
Date: Wed, 17 Jul 2024 13:55:50 -0500
From: Stuart Hayes <stuart.w.hayes@...il.com>
To: linux-kernel@...r.kernel.org,
Keith Busch <kbusch@...nel.org>,
Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@....de>,
Sagi Grimberg <sagi@...mberg.me>,
linux-nvme@...ts.infradead.org
Cc: Hannes Reinecke <hare@...e.de>,
Martin Wilck <martin.wilck@...e.com>,
Ayush Siddarath <ayush.siddarath@...l.com>,
Stuart Hayes <stuart.w.hayes@...il.com>
Subject: [PATCH v4] nvme_core: scan namespaces asynchronously
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 <stuart.w.hayes@...il.com>
---
changes from V3:
* changed "next_idx" to "next_nsid" in async_scan_info (cosmetic)
* added comments to struct async_scan_info
* changed nvme_scan_ns_list() to use local ns_list pointer
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 | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 782090ce0bc1..dc43146dc03d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4,6 +4,7 @@
* Copyright (c) 2011-2014, Intel Corporation.
*/
+#include <linux/async.h>
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
#include <linux/blk-integrity.h>
@@ -3952,6 +3953,35 @@ 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_nsid: Index of next NSID to scan in ns_list
+ * @ns_list: Pointer to list of NSIDs to scan
+ *
+ * Note: There is a single async_scan_info structure shared by all instances
+ * of nvme_scan_ns_async() scanning a given controller, so the atomic
+ * operations on next_nsid are critical to ensure each instance scans a unique
+ * NSID.
+ */
+struct async_scan_info {
+ struct nvme_ctrl *ctrl;
+ atomic_t next_nsid;
+ __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_nsid);
+ 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)
{
@@ -3978,11 +4008,15 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl)
__le32 *ns_list;
u32 prev = 0;
int ret = 0, i;
+ ASYNC_DOMAIN(domain);
+ struct async_scan_info scan_info;
ns_list = kzalloc(NVME_IDENTIFY_DATA_SIZE, GFP_KERNEL);
if (!ns_list)
return -ENOMEM;
+ scan_info.ctrl = ctrl;
+ scan_info.ns_list = ns_list;
for (;;) {
struct nvme_command cmd = {
.identify.opcode = nvme_admin_identify,
@@ -3998,19 +4032,23 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl)
goto free;
}
+ atomic_set(&scan_info.next_nsid, 0);
for (i = 0; i < nr_entries; i++) {
u32 nsid = le32_to_cpu(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);
}
out:
nvme_remove_invalid_namespaces(ctrl, prev);
free:
+ async_synchronize_full_domain(&domain);
kfree(ns_list);
return ret;
}
--
2.39.3
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