From: Hannes Reinecke <hare@suse.de>
To: Sagi Grimberg <sagi@grimberg.me>,
mwilck@suse.com, Christoph Hellwig <hch@lst.de>,
Keith Busch <keith.busch@intel.com>
Cc: marting@netapp.com, linux-nvme@lists.infradead.org
Subject: Re: [PATCH 1/2] nvme: multipath: round-robin: fix logic for non-optimized paths
Date: Wed, 22 Jul 2020 07:35:03 +0200 [thread overview]
Message-ID: <c8890576-31e5-a56c-53ab-b953b7e404b7@suse.de> (raw)
In-Reply-To: <c51e7fa1-2e89-e5e1-6962-bc16470afd59@grimberg.me>
On 7/21/20 7:19 PM, Sagi Grimberg wrote:
>
>>>> Handle the special case where we have exactly one optimized path,
>>>> which we should keep using in this case. Also, use the next
>>>> non-optimized path, not the last one.
>>>
>>> Not sure I understand, does this patch also use nonopt paths if we
>>> have a single opt path?
>>
>> Indeed, the latter change should be removed from this patch.
>
> Why should we even do this? we have a clear indication from the
> controller on ns access. If we have a optimized path we should never
> select any non-optimized path.
>
> What if a non-optimized path has a 50x higher access latency? it's just
> wrong to use this path...
Errm. I think Martin didn't state clearly what the problem was.
The problem is when the _current_ path is the only optimized path, and
all other paths are non-optimized:
for (ns = nvme_next_ns(head, old);
ns != old;
ns = nvme_next_ns(head, ns)) {
We start with the _next_ path, and stop _before_ we check the 'old'
path. Consequently the 'old' path is never checked, and never selected.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
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prev parent reply other threads:[~2020-07-22 5:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 19:59 [PATCH 1/2] nvme: multipath: round-robin: fix logic for non-optimized paths mwilck
2020-07-16 19:59 ` [PATCH 2/2] nvme: multipath: round-robin: don't fall back to numa mwilck
2020-07-17 6:10 ` Hannes Reinecke
2020-07-17 6:08 ` [PATCH 1/2] nvme: multipath: round-robin: fix logic for non-optimized paths Hannes Reinecke
2020-07-20 19:51 ` Sagi Grimberg
2020-07-21 6:39 ` Hannes Reinecke
2020-07-21 17:19 ` Sagi Grimberg
2020-07-22 5:35 ` Hannes Reinecke [this message]
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