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Date: Thu, 23 May 2024 08:28:27 +0200
From: Hannes Reinecke <hare@...e.de>
To: Chaitanya Kulkarni <chaitanyak@...dia.com>,
John Meneghini <jmeneghi@...hat.com>, "emilne@...hat.com" <emilne@...hat.com>
Cc: "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
"hch@....de" <hch@....de>, "sagi@...mberg.me" <sagi@...mberg.me>,
"kbusch@...nel.org" <kbusch@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"jrani@...estorage.com" <jrani@...estorage.com>,
"randyj@...estorage.com" <randyj@...estorage.com>,
"hare@...nel.org" <hare@...nel.org>
Subject: Re: [PATCH v5] nvme: multipath: Implemented new iopolicy
"queue-depth"
On 5/23/24 06:29, Chaitanya Kulkarni wrote:
> On 5/22/24 09:54, John Meneghini wrote:
>> From: "Ewan D. Milne" <emilne@...hat.com>
>>
>> The round-robin path selector is inefficient in cases where there is a
>> difference in latency between paths. In the presence of one or more
>> high latency paths the round-robin selector continues to use the high
>> latency path equally. This results in a bias towards the highest latency
>> path and can cause a significant decrease in overall performance as IOs
>> pile on the highest latency path. This problem is acute with NVMe-oF
>> controllers.
>>
>> The queue-depth policy instead sends I/O requests down the path with the
>> least amount of requests in its request queue. Paths with lower latency
>> will clear requests more quickly and have less requests in their queues
>> compared to higher latency paths. The goal of this path selector is to
>> make more use of lower latency paths which will bring down overall IO
>> latency and increase throughput and performance.
>>
>> Signed-off-by: Thomas Song <tsong@...estorage.com>
>> [emilne: patch developed by Thomas Song @ Pure Storage, fixed whitespace
>> and compilation warnings, updated MODULE_PARM description, and
>> fixed potential issue with ->current_path[] being used]
>> Signed-off-by: Ewan D. Milne <emilne@...hat.com>
>> [jmeneghi: vairious changes and improvements, addressed review comments]
>> Signed-off-by: John Meneghini <jmeneghi@...hat.com>
>> Link: https://lore.kernel.org/linux-nvme/20240509202929.831680-1-jmeneghi@redhat.com/
>> Tested-by: Marco Patalano <mpatalan@...hat.com>
>> Reviewed-by: Randy Jennings <randyj@...estorage.com>
>> Tested-by: Jyoti Rani <jrani@...estorage.com>
>> ---
>
> [...]
>
>> +static struct nvme_ns *nvme_queue_depth_path(struct nvme_ns_head *head)
>> +{
>> + struct nvme_ns *best_opt = NULL, *best_nonopt = NULL, *ns;
>> + unsigned int min_depth_opt = UINT_MAX, min_depth_nonopt = UINT_MAX;
>> + unsigned int depth;
>> +
>> + list_for_each_entry_rcu(ns, &head->list, siblings) {
>> + if (nvme_path_is_disabled(ns))
>> + continue;
>> +
>> + depth = atomic_read(&ns->ctrl->nr_active);
>> +
>> + switch (ns->ana_state) {
>> + case NVME_ANA_OPTIMIZED:
>> + if (depth < min_depth_opt) {
>> + min_depth_opt = depth;
>> + best_opt = ns;
>> + }
>> + break;
>> +
>
> nit:- no need to add white line needed after break above ?
>
>> + case NVME_ANA_NONOPTIMIZED:
>> + if (depth < min_depth_nonopt) {
>> + min_depth_nonopt = depth;
>> + best_nonopt = ns;
>> + }
>> + break;
>> + default:
>> + break;
>> + }
>> +
>> + if (min_depth_opt == 0)
>> + return best_opt;
>> + }
>> +
>> + return best_opt ? best_opt : best_nonopt;
>> +}
>> +
>>
>
> [...]
>
>> @@ -800,6 +860,29 @@ static ssize_t nvme_subsys_iopolicy_show(struct device *dev,
>> nvme_iopolicy_names[READ_ONCE(subsys->iopolicy)]);
>> }
>>
>> +static void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy)
>
> nit:- overly long line, as rest of the file is < 80 char par line ?
>
>> +{
>> + struct nvme_ctrl *ctrl;
>> + int old_iopolicy = READ_ONCE(subsys->iopolicy);
>> +
>> + if (old_iopolicy == iopolicy)
>> + return;
>> +
>> + WRITE_ONCE(subsys->iopolicy, iopolicy);
>> +
>> + /* iopolicy changes reset the counters and clear the mpath by design */
>> + mutex_lock(&nvme_subsystems_lock);
>> + list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
>> + atomic_set(&ctrl->nr_active, 0);
>> + nvme_mpath_clear_ctrl_paths(ctrl);
>> + }
>> + mutex_unlock(&nvme_subsystems_lock);
>> +
>> + pr_notice("%s: changed from %s to %s for subsysnqn %s\n", __func__,
>> + nvme_iopolicy_names[old_iopolicy], nvme_iopolicy_names[iopolicy],
>
> nit: overly long line above as rest of the file is < 80 char ...
>
> As far as I remember, most of the nvme code uses pr_info(), but if
> decision has been made to use pr_notice() for a specific reason then
> please ignore this comment.
>
>> + subsys->subnqn);
>> +}
>> +
>
> [...]
>
>> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
>> index fc31bd340a63..fa3833d88a85 100644
>> --- a/drivers/nvme/host/nvme.h
>> +++ b/drivers/nvme/host/nvme.h
>> @@ -50,6 +50,8 @@ extern struct workqueue_struct *nvme_wq;
>> extern struct workqueue_struct *nvme_reset_wq;
>> extern struct workqueue_struct *nvme_delete_wq;
>>
>> +extern struct mutex nvme_subsystems_lock;
>> +
>> /*
>> * List of workarounds for devices that required behavior not specified in
>> * the standard.
>> @@ -195,6 +197,7 @@ enum {
>> NVME_REQ_CANCELLED = (1 << 0),
>> NVME_REQ_USERCMD = (1 << 1),
>> NVME_MPATH_IO_STATS = (1 << 2),
>> + NVME_MPATH_CNT_ACTIVE = (1 << 3),
>
> nit:- I think we need to align above line to rest of the members in
> this enum ...
>
>> };
>>
>> static inline struct nvme_request *nvme_req(struct request *req)
>> @@ -359,6 +362,7 @@ struct nvme_ctrl {
>> size_t ana_log_size;
>> struct timer_list anatt_timer;
>> struct work_struct ana_work;
>> + atomic_t nr_active;
>> #endif
>>
>> #ifdef CONFIG_NVME_HOST_AUTH
>> @@ -407,6 +411,7 @@ static inline enum nvme_ctrl_state nvme_ctrl_state(struct nvme_ctrl *ctrl)
>> enum nvme_iopolicy {
>> NVME_IOPOLICY_NUMA,
>> NVME_IOPOLICY_RR,
>> + NVME_IOPOLICY_QD,
>> };
>>
>> struct nvme_subsystem {
>
> apart from the few nits patch does looks good to me.
>
> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
>
> not a blocker to merge this patch, but we need a blktests for this code
> in nvme
> category ...
>
As presented at LSF by Daniel; ALUA support (and, with that, multipath
support) is one of the topics to be implemented for blktests.
And without that we can't have a meaningful QD test.
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@...e.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
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