From: Changheun Lee <nanich.lee@samsung.com>
To: ming.lei@redhat.com
Cc: Damien.LeMoal@wdc.com, Johannes.Thumshirn@wdc.com,
asml.silence@gmail.com, axboe@kernel.dk, bvanassche@acm.org,
gregkh@linuxfoundation.org, hch@infradead.org,
jisoo2146.oh@samsung.com, junho89.kim@samsung.com,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
mj0123.lee@samsung.com, nanich.lee@samsung.com, osandov@fb.com,
patchwork-bot@kernel.org, seunghwan.hyun@samsung.com,
sookwan7.kim@samsung.com, tj@kernel.org, tom.leiming@gmail.com,
woosung2.lee@samsung.com, yt0928.kim@samsung.com
Subject: Re: [RESEND,v5,1/2] bio: limit bio max size
Date: Tue, 13 Apr 2021 13:37:33 +0900 [thread overview]
Message-ID: <20210413043733.28880-1-nanich.lee@samsung.com> (raw)
In-Reply-To: <YHO9LQUt1e0J6+l9@T590>
> On Sun, Apr 11, 2021 at 10:13:01PM +0000, Damien Le Moal wrote:
> > On 2021/04/09 23:47, Bart Van Assche wrote:
> > > On 4/7/21 3:27 AM, Damien Le Moal wrote:
> > >> On 2021/04/07 18:46, Changheun Lee wrote:
> > >>> I'll prepare new patch as you recommand. It will be added setting of
> > >>> limit_bio_size automatically when queue max sectors is determined.
> > >>
> > >> Please do that in the driver for the HW that benefits from it. Do not do this
> > >> for all block devices.
> > >
> > > Hmm ... is it ever useful to build a bio with a size that exceeds
> > > max_hw_sectors when submitting a bio directly to a block device, or in
> > > other words, if no stacked block driver sits between the submitter and
> > > the block device? Am I perhaps missing something?
> >
> > Device performance wise, the benefits are certainly not obvious to me either.
> > But for very fast block devices, I think the CPU overhead of building more
> > smaller BIOs may be significant compared to splitting a large BIO into multiple
> > requests. Though it may be good to revisit this with some benchmark numbers.
>
> This patch tries to address issue[1] in do_direct_IO() in which
> Changheun observed that other operations takes time between adding page
> to bio.
>
> However, do_direct_IO() just does following except for adding bio and
> submitting bio:
>
> - retrieves pages at batch(pin 64 pages each time from VM) and
>
> - retrieve block mapping(get_more_blocks), which is still done usually
> very less times for 32MB; for new mapping, clean_bdev_aliases() may
> take a bit time.
>
> If there isn't system memory pressure, pin 64 pages won't be slow, but
> get_more_blocks() may take a bit time.
>
> Changheun, can you check if multiple get_more_blocks() is called for submitting
> 32MB in your test?
almost one time called.
>
> In my 32MB sync dio f2fs test on x86_64 VM, one buffer_head mapping can
> hold 32MB, but it is one freshly new f2fs.
>
> I'd suggest to understand the issue completely before figuring out one
> solution.
Thank you for your advice. I'll analyze more about your point later. :)
But I think it's different from finding main time spend point in
do_direct_IO(). I think excessive loop should be controlled.
8,192 loops in do_direct_IO() - for 32MB - to submit one bio is too much
on 4KB page system. I want to apply a optional solution to avoid
excessive loop casued by multipage bvec.
Thanks,
Changheun Lee
next prev parent reply other threads:[~2021-04-13 4:55 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20210316080104epcas1p11483035c927c2e65600ae90309334b24@epcas1p1.samsung.com>
2021-03-16 7:44 ` [RESEND PATCH v5 1/2] bio: limit bio max size Changheun Lee
[not found] ` <CGME20210316080106epcas1p3522dda95e9c97fc39b40b008bbf87c04@epcas1p3.samsung.com>
2021-03-16 7:44 ` [RESEND PATCH v5 2/2] bio: add limit_bio_size sysfs Changheun Lee
2021-04-06 21:05 ` Bart Van Assche
[not found] ` <CGME20210407013850epcas1p2d305f138c9fa1431abba1ec44a382de9@epcas1p2.samsung.com>
2021-04-07 1:21 ` Changheun Lee
2021-04-07 5:43 ` Greg KH
[not found] ` <CGME20210406014905epcas1p16830a46b7ac6af95a0e2c2c6f4c04859@epcas1p1.samsung.com>
2021-04-06 1:31 ` [RESEND PATCH v5 1/2] bio: limit bio max size Changheun Lee
2021-04-06 7:32 ` Greg KH
[not found] ` <CGME20210407003345epcas1p21376df37d3dfe933684139d3beaf9c51@epcas1p2.samsung.com>
2021-04-07 0:16 ` Changheun Lee
2021-04-07 5:05 ` Greg KH
[not found] ` <CGME20210407052407epcas1p1d0b5d23ac04a68760f691954e7ada3dd@epcas1p1.samsung.com>
2021-04-07 5:06 ` Changheun Lee
2021-04-07 5:36 ` Greg KH
[not found] ` <CGME20210407071241epcas1p2559ea674299b686c9001326894c933bc@epcas1p2.samsung.com>
2021-04-07 6:55 ` Changheun Lee
2021-04-07 7:40 ` Greg KH
[not found] ` <CGME20210407094610epcas1p472207e8d3ca0e5e697974c993a2a34f7@epcas1p4.samsung.com>
2021-04-07 9:28 ` [RESEND,v5,1/2] " Changheun Lee
2021-04-07 10:27 ` Damien Le Moal
2021-04-09 14:47 ` Bart Van Assche
2021-04-11 22:13 ` Damien Le Moal
2021-04-12 3:23 ` Ming Lei
[not found] ` <CGME20210413045517epcas1p32b058646dd795e59389401ca997c4cac@epcas1p3.samsung.com>
2021-04-13 4:37 ` Changheun Lee [this message]
2021-04-13 5:32 ` Christoph Hellwig
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