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From: Zhaoyang Huang <huangzhaoyang@gmail.com>
Date: Tue, 14 May 2024 10:37:34 +0800
Message-ID: <CAGWkznGYBAWQCBFRbFCVkFcUZsZ77+yf+Pun6NS8EpmdKdsaBQ@mail.gmail.com>
Subject: Re: [RFC PATCH 2/2] mm: introduce budgt control in readahead
To: Matthew Wilcox <willy@infradead.org>
Cc: "zhaoyang.huang" <zhaoyang.huang@unisoc.com>, Andrew Morton <akpm@linux-foundation.org>, 
	Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>, 
	Baolin Wang <baolin.wang@linux.alibaba.com>, linux-mm@kvack.org, 
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, 
	cgroups@vger.kernel.org, steve.kang@unisoc.com
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On Sat, May 11, 2024 at 3:35=E2=80=AFPM Zhaoyang Huang <huangzhaoyang@gmail=
com> wrote:
>
> On Fri, May 10, 2024 at 11:18=E2=80=AFAM Matthew Wilcox <willy@infradead.=
org> wrote:
> >
> > On Fri, May 10, 2024 at 10:43:20AM +0800, Zhaoyang Huang wrote:
> > > Thanks for the prompt. I did some basic research on soft RAID and
> > > wonder if applying the bps limit on /dev/md0 like below could make
> > > this work.
> >
> > No.  Look at btrfs' raid support, for example.  it doesn't use md0.
> If I understand the below command correctly, btrfs uses one of the
> volumes within RAID as the mount block device, not /dev/md0. However,
> I think this is a problem of blkio.throttle rather than this commit
> which means this readahead budget control will work accordingly as
> long as blkio.throttle's parameter is configured correctly(eg. 50/50
> on sdb and sdc)
>
> mkfs.btrfs -m raid0 -d raid0 /dev/sdb /dev/sdc
> mount -t btrfs /dev/sdb /mnt/btr
>
>
>
> >
> > > I didn't find information about 'RAID internally'. Could we set the
> > > limit on the root device(the one used for mount) to manage the whole
> > > partition without caring about where the bio finally goes? Or ask the
> > > user to decide if to use by making sure the device they apply will no=
t
> > > do RAID?
> >
> > No.

@all, Please find below for more test results where we can find this
commit has the result meet the desired value more closely and enhance
it by 3% than mainline.

echo "254:48 20000000" > blkio.throttle.read_bps_device
fio -filename=3D/data/ylog/ap/000-0101_000015_poweron.ylog -rw=3Dread
-direct=3D0 -bs=3D4k -size=3D2000M -numjobs=3D8 -group_reporting -name=3Dmy=
test

    before : IOPS=3D37.9k, BW=3D148MiB/s (155MB/s)(11.6GiB/80333msec)
    after  : IOPS=3D39.0k, BW=3D153MiB/s (160MB/s)(15.6GiB/104914msec)

    before : clat (usec): min=3D4, max=3D1056.6k, avg=3D197.23, stdev=3D100=
80.69
    after  : clat (usec): min=3D4, max=3D193481, avg=3D188.83, stdev=3D4651=
29

    before : lat (usec): min=3D5, max=3D1056.6k, avg=3D200.48, stdev=3D1008=
0.76
    after  : lat (usec): min=3D5, max=3D193483, avg=3D192.68, stdev=3D4651.=
87


echo "254:48 30000000" > blkio.throttle.read_bps_device
fio -filename=3D/data/ylog/ap/000-0101_000015_poweron.ylog -rw=3Dread
-direct=3D0 -bs=3D4k -size=3D2000M -numjobs=3D8 -group_reporting -name=3Dmy=
test

    before : IOPS=3D57.2k, BW=3D224MiB/s (234MB/s)(15.6GiB/71561msec)
    after  : IOPS=3D58.5k, BW=3D229MiB/s (240MB/s)(15.6GiB/69996msec)

    before : clat (usec): min=3D4, max=3D1105.5k, avg=3D126.20, stdev=3D641=
9.22
    after  : clat (usec): min=3D4, max=3D183956, avg=3D120.60, stdev=3D2957=
28

    before : lat (usec): min=3D5, max=3D1105.5k, avg=3D129.45, stdev=3D6419=
29
    after  : lat (usec): min=3D5, max=3D183958, avg=3D124.40, stdev=3D2958.=
18