Re: [PATCH 2/2] nvme-multipath: do not fall back to __nvme_find_path() for non-optimized paths

[Hannes Reinecke <hare@suse.de>]

On 7/28/20 10:16 AM, Christoph Hellwig wrote:
> On Tue, Jul 28, 2020 at 10:14:14AM +0200, Hannes Reinecke wrote:
>> On 7/28/20 10:02 AM, Christoph Hellwig wrote:
>>> On Tue, Jul 28, 2020 at 08:25:18AM +0200, Hannes Reinecke wrote:
>>>>> Maybe instead of the early return put the following condition on else?
>>>>
>>>> That depends on whether we want to have a fallback to __nvme_find_path() or 
>>>> not. With your suggestion we would lose that; I'd rather keep it.
>>>
>>> Why would we want to fall back?  nvme_round_robin_path only
>>> returns NULL in case there is a single disabled path, in which
>>> case __nvme_find_path won't find anything either.  I'd go for something
>>> like this:
>>>
>>> ---
>>> From 4f578364a3d15898c7d715315a3371b2f71db416 Mon Sep 17 00:00:00 2001
>>> From: Hannes Reinecke <hare@suse.de>
>>> Date: Mon, 27 Jul 2020 18:08:03 +0200
>>> Subject: nvme-multipath: do not fall back to __nvme_find_path() for
>>>  non-optimized paths
>>>
>>> When nvme_round_robin_path() finds a valid namespace we should be using it;
>>> falling back to __nvme_find_path() for non-optimized paths will cause the
>>> result from nvme_round_robin_path() to be ignored for non-optimized paths.
>>>
>>> Signed-off-by: Martin Wilck <mwilck@suse.com>
>>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>>> Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> ---
>>>  drivers/nvme/host/multipath.c | 11 +++++++----
>>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
>>> index 93c70e1591de8f..3ded54d2c9c6ad 100644
>>> --- a/drivers/nvme/host/multipath.c
>>> +++ b/drivers/nvme/host/multipath.c
>>> @@ -281,10 +281,13 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
>>>  	struct nvme_ns *ns;
>>>  
>>>  	ns = srcu_dereference(head->current_path[node], &head->srcu);
>>> -	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR && ns)
>>> -		ns = nvme_round_robin_path(head, node, ns);
>>> -	if (unlikely(!ns || !nvme_path_is_optimized(ns)))
>>> -		ns = __nvme_find_path(head, node);
>>> +	if (unlikely(!ns))
>>> +		return __nvme_find_path(head, node);
>>> +
>>> +	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
>>> +		return nvme_round_robin_path(head, node, ns);
>>> +	if (unlikely(!nvme_path_is_optimized(ns)))
>>> +		return __nvme_find_path(head, node);
>>>  	return ns;
>>>  }
>>>  
>>>
>>
>> Yes, that would work, too.
>>
>> Should I resend?
> 
> No need, I can apply it with the modification.   But if you have a
> RR test setup it would be great to run it through that again, just in
> case.
> 
I'm at it.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

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