From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <kbusch@kernel.org>,
Max Gurtovoy <mgurtovoy@nvidia.com>,
linux-nvme@lists.infradead.org,
Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH rfc] nvme: support io stats on the mpath device
Date: Tue, 25 Oct 2022 18:58:19 +0300 [thread overview]
Message-ID: <f214dff7-9562-5f32-38b3-51bfc1216e98@grimberg.me> (raw)
In-Reply-To: <20221025153017.GA24137@lst.de>
>>> make up the multipath device. Only the low-level driver can do that right now,
>>> so perhaps either call into the driver to get all the block_device parts, or
>>> the gendisk needs to maintain a list of those parts itself.
>>
>> I definitely don't think we want to propagate the device relationship to
>> blk-mq. But a callback to the driver also seems very niche to nvme
>> multipath and is also kinda messy to combine calculations like
>> iops/bw/latency accurately which depends on the submission distribution
>> to the bottom devices which we would need to track now.
>>
>> I'm leaning towards just moving forward with this, take the relatively
>> small hit, and if people absolutely care about the extra latency, then
>> they can disable it altogether (upper and/or bottom devices).
>
> So looking at the patches I'm really not a big fan of the extra
> accounting calls, and especially the start_time field in the
> nvme_request
Don't love it either.
> and even more so the special start/end calls in all
> the transport drivers.
The end is centralized and the start part has not sprinkled to
the drivers. I don't think its bad.
> the stats sysfs attributes already have the entirely separate
> blk-mq vs bio based code pathes. So I think having a block_device
> operation that replaces part_stat_read_all which allows nvme to
> iterate over all pathes and collect the numbers would seem
> a lot nicer. There might be some caveats like having to stash
> away the numbers for disappearing paths, though.
You think this is better? really? I don't agree with you, I think its
better to pay a small cost than doing this very specialized thing that
will only ever be used for nvme-mpath.
next prev parent reply other threads:[~2022-10-25 15:58 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-28 19:55 [PATCH rfc 0/1] nvme-mpath: Add IO stats support Sagi Grimberg
2022-09-28 19:55 ` [PATCH rfc] nvme: support io stats on the mpath device Sagi Grimberg
2022-09-29 9:42 ` Max Gurtovoy
2022-09-29 9:59 ` Sagi Grimberg
2022-09-29 10:25 ` Max Gurtovoy
2022-09-29 15:03 ` Keith Busch
2022-09-29 16:14 ` Sagi Grimberg
2022-09-30 15:21 ` Keith Busch
2022-10-03 8:09 ` Sagi Grimberg
2022-10-25 15:30 ` Christoph Hellwig
2022-10-25 15:58 ` Sagi Grimberg [this message]
2022-10-30 16:22 ` Christoph Hellwig
2022-09-29 16:32 ` Sagi Grimberg
2022-09-30 15:16 ` Keith Busch
2022-10-03 8:02 ` Sagi Grimberg
2022-10-03 9:32 ` Sagi Grimberg
2022-09-29 15:05 ` Jens Axboe
2022-09-29 16:25 ` Sagi Grimberg
2022-09-30 0:08 ` Jens Axboe
2022-10-03 8:35 ` Sagi Grimberg
2022-09-29 10:04 ` Sagi Grimberg
2022-09-29 15:07 ` Jens Axboe
2022-10-03 8:38 ` Sagi Grimberg
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f214dff7-9562-5f32-38b3-51bfc1216e98@grimberg.me \
--to=sagi@grimberg.me \
--cc=Chaitanya.Kulkarni@wdc.com \
--cc=axboe@kernel.dk \
--cc=hare@suse.de \
--cc=hch@lst.de \
--cc=kbusch@kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-nvme@lists.infradead.org \
--cc=mgurtovoy@nvidia.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).