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Message-ID: <7c2451ad-2d6d-4517-9373-0f5d58f2cfad@gmail.com>
Date: Wed, 24 Jan 2024 13:38:36 -0600
From: stuart hayes <stuart.w.hayes@...il.com>
To: Sagi Grimberg <sagi@...mberg.me>, 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 1/22/2024 3:13 AM, Sagi Grimberg wrote:
>
>
> 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.
Thank you for the feedback on the patch, I agree with it.
I'm not sure how to implement a blktest suite for this, though. I can look into it.
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