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Message-ID: <189cde89-9750-476f-8fbb-1c95dc056efb@grimberg.me>
Date: Mon, 22 Jan 2024 11:13:15 +0200
From: Sagi Grimberg <sagi@...mberg.me>
To: Stuart Hayes <stuart.w.hayes@...il.com>, linux-kernel@...r.kernel.org,
Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@....de>, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v2] nvme_core: scan namespaces asynchronously
On 1/18/24 23:03, 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.
>
> The time it took for all namespaces to show up after connecting (via TCP)
> to a controller with 1002 namespaces was measured:
>
> network latency without patch with patch
> 0 6s 1s
> 50ms 210s 10s
> 100ms 417s 18s
>
Impressive speedup. Not a very common use-case though...
> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
>
> --
> V2: remove module param to enable/disable async scanning
> add scan time measurements to commit message
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 0af612387083..069350f85b83 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>
> @@ -3812,12 +3813,38 @@ static void nvme_validate_ns(struct nvme_ns *ns, struct nvme_ns_info *info)
> nvme_ns_remove(ns);
> }
>
> -static void nvme_scan_ns(struct nvme_ctrl *ctrl, unsigned nsid)
> +/*
> + * struct nvme_scan_state - keeps track of controller & NSIDs to scan
> + * @ctrl: Controller on which namespaces are being scanned
> + * @count: Next NSID to scan (for sequential scan), or
> + * Index of next NSID to scan in ns_list (for list scan)
> + * @ns_list: pointer to list of NSIDs to scan (NULL if sequential scan)
> + */
> +struct nvme_scan_state {
> + struct nvme_ctrl *ctrl;
> + atomic_t count;
> + __le32 *ns_list;
> +};
> +
> +static void nvme_scan_ns(void *data, async_cookie_t cookie)
I think its better to call it nvme_scan_ns_async to indicate what
it is.
> {
> - struct nvme_ns_info info = { .nsid = nsid };
> + struct nvme_ns_info info = {};
> + struct nvme_scan_state *scan_state;
> + struct nvme_ctrl *ctrl;
> + u32 nsid;
> struct nvme_ns *ns;
> int ret;
>
> + scan_state = data;
> + ctrl = scan_state->ctrl;
I think these assignments can be done on the declaration.
> + nsid = (u32)atomic_fetch_add(1, &scan_state->count);
> + /*
> + * get NSID from list (if scanning from a list, not sequentially)
> + */
> + if (scan_state->ns_list)
> + nsid = le32_to_cpu(scan_state->ns_list[nsid]);
> +
This is awkward. ns_list passed in optionally.
How about we limit this change to only operate on nvme_scan_ns_list?
If the controller is old or quirked to support only a sequential scan
it does not benefit from a parallel scan. I doubt that these controllers
are likely to expose a large number of namespaces anyways.
> + info.nsid = nsid;
> if (nvme_identify_ns_descs(ctrl, &info))
> return;
>
> @@ -3881,11 +3908,15 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl)
> __le32 *ns_list;
> u32 prev = 0;
> int ret = 0, i;
> + ASYNC_DOMAIN(domain);
> + struct nvme_scan_state scan_state;
>
> ns_list = kzalloc(NVME_IDENTIFY_DATA_SIZE, GFP_KERNEL);
> if (!ns_list)
> return -ENOMEM;
>
> + scan_state.ctrl = ctrl;
> + scan_state.ns_list = ns_list;
Is there a need to have a local ns_list variable here?
> for (;;) {
> struct nvme_command cmd = {
> .identify.opcode = nvme_admin_identify,
> @@ -3901,19 +3932,25 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl)
> goto free;
> }
>
> + /*
> + * scan list starting at list offset 0
> + */
> + atomic_set(&scan_state.count, 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, &scan_state, &domain);
> while (++prev < nsid)
> nvme_ns_remove_by_nsid(ctrl, prev);
> }
> + async_synchronize_full_domain(&domain);
> }
> out:
> nvme_remove_invalid_namespaces(ctrl, prev);
Is it a good idea to remove the invalid namespaces before synchronizing
the async scans?
> free:
> + async_synchronize_full_domain(&domain);
> kfree(ns_list);
> return ret;
> }
> @@ -3922,14 +3959,23 @@ static void nvme_scan_ns_sequential(struct nvme_ctrl *ctrl)
> {
> struct nvme_id_ctrl *id;
> u32 nn, i;
> + ASYNC_DOMAIN(domain);
> + struct nvme_scan_state scan_state;
>
> if (nvme_identify_ctrl(ctrl, &id))
> return;
> nn = le32_to_cpu(id->nn);
> kfree(id);
>
> + scan_state.ctrl = ctrl;
> + /*
> + * scan sequentially starting at NSID 1
> + */
> + atomic_set(&scan_state.count, 1);
> + scan_state.ns_list = NULL;
> for (i = 1; i <= nn; i++)
> - nvme_scan_ns(ctrl, i);
> + async_schedule_domain(nvme_scan_ns, &scan_state, &domain);
> + async_synchronize_full_domain(&domain);
>
> nvme_remove_invalid_namespaces(ctrl, nn);
> }
I think we need a blktest for this. ns scanning has been notorious when
running simultaneously with controller reset/reconnect/remove
sequences... Ideally a test with a larger number of namespaces to
exercise the code.
Also, make sure that blktest suite does not complain about anything
else.
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