From: Keith Busch <kbusch@kernel.org>
To: Sagi Grimberg <sagi@grimberg.me>
Cc: Max Gurtovoy <mgurtovoy@nvidia.com>,
linux-nvme@lists.infradead.org, Christoph Hellwig <hch@lst.de>,
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: Fri, 30 Sep 2022 09:21:25 -0600 [thread overview]
Message-ID: <YzcJdeR82tHbFGAh@kbusch-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <1b7feff8-48a4-6cd2-5a44-28a499630132@grimberg.me>
On Thu, Sep 29, 2022 at 07:14:23PM +0300, Sagi Grimberg wrote:
>
> > > > 3. Do you have some performance numbers (we're touching the fast path
> > > > here) ?
> > >
> > > This is pretty light-weight, accounting is per-cpu and only wrapped by
> > > preemption disable. This is a very small price to pay for what we gain.
> >
> > It does add up, though, and some environments disable stats to skip the
> > overhead. At a minimum, you need to add a check for blk_queue_io_stat() before
> > assuming you need to account for stats.
> >
> > Instead of duplicating the accounting, could you just have the stats file report
> > the sum of its hidden devices?
>
> Interesting...
>
> How do you suggest we do that? .collect_stats() callout in fops?
Maybe, yeah. I think we'd need something to enumerate the HIDDEN disks that
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.
next prev parent reply other threads:[~2022-09-30 15:21 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 [this message]
2022-10-03 8:09 ` Sagi Grimberg
2022-10-25 15:30 ` Christoph Hellwig
2022-10-25 15:58 ` Sagi Grimberg
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
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