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From: Andrea Vai <andrea.vai@unipv.it>
To: Ming Lei <ming.lei@redhat.com>, "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: "Schmid, Carsten" <Carsten_Schmid@mentor.com>,
	Finn Thain <fthain@telegraphics.com.au>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Jens Axboe <axboe@kernel.dk>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	USB list <linux-usb@vger.kernel.org>,
	SCSI development list <linux-scsi@vger.kernel.org>,
	Himanshu Madhani <himanshu.madhani@cavium.com>,
	Hannes Reinecke <hare@suse.com>, Omar Sandoval <osandov@fb.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Hans Holmberg <Hans.Holmberg@wdc.com>,
	Kernel development list <linux-kernel@vger.kernel.org>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
Date: Tue, 07 Jan 2020 08:51:41 +0100
Message-ID: <5bd51904b1b6511748c5454bce437bdc038eeb1f.camel@unipv.it> (raw)
In-Reply-To: <20191226083706.GA17974@ming.t460p>

Il giorno gio, 26/12/2019 alle 16.37 +0800, Ming Lei ha scritto:
> On Wed, Dec 25, 2019 at 10:30:57PM -0500, Theodore Y. Ts'o wrote:
> > On Thu, Dec 26, 2019 at 10:27:02AM +0800, Ming Lei wrote:
> > > Maybe we need to be careful for HDD., since the request count in
> scheduler
> > > queue is double of in-flight request count, and in theory NCQ
> should only
> > > cover all in-flight 32 requests. I will find a sata HDD., and
> see if
> > > performance drop can be observed in the similar 'cp' test.
> > 
> > Please try to measure it, but I'd be really surprised if it's
> > significant with with modern HDD's.
> 
> Just find one machine with AHCI SATA, and run the following xfs
> overwrite test:
> 
> #!/bin/bash
> DIR=$1
> echo 3 > /proc/sys/vm/drop_caches
> fio --readwrite=write --filesize=5g --overwrite=1 --
> filename=$DIR/fiofile \
>         --runtime=60s --time_based --ioengine=psync --direct=0 --
> bs=4k
> 		--iodepth=128 --numjobs=2 --group_reporting=1 --
> name=overwrite
> 
> FS is xfs, and disk is LVM over AHCI SATA with NCQ(depth 32),
> because the
> machine is picked up from RH beaker, and it is the only disk in the
> box.
> 
> #lsblk
> NAME                            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
> sda                               8:0    0 931.5G  0 disk 
> ├─sda1                            8:1    0     1G  0 part /boot
> └─sda2                            8:2    0 930.5G  0 part 
>   ├─rhel_hpe--ml10gen9--01-root 253:0    0    50G  0 lvm  /
>   ├─rhel_hpe--ml10gen9--01-swap 253:1    0   3.9G  0 lvm  [SWAP]
>   └─rhel_hpe--ml10gen9--01-home 253:2    0 876.6G  0 lvm  /home
> 
> 
> kernel: 3a7ea2c483a53fc("scsi: provide mq_ops->busy() hook") which
> is
> the previous commit of f664a3cc17b7 ("scsi: kill off the legacy IO
> path").
> 
>             |scsi_mod.use_blk_mq=N |scsi_mod.use_blk_mq=Y |
> -----------------------------------------------------------
> throughput: |244MB/s               |169MB/s               |
> -----------------------------------------------------------
> 
> Similar result can be observed on v5.4 kernel(184MB/s) with same
> test
> steps.
> 
> 
> > That because they typically have
> > a queue depth of 16, and a max_sectors_kb of 32767 (e.g., just
> under
> > 32 MiB).  Sort seeks are typically 1-2 ms, with full stroke seeks
> > 8-10ms.  Typical sequential write speeds on a 7200 RPM drive is
> > 125-150 MiB/s.  So suppose every other request sent to the HDD is
> from
> > the other request stream.  The disk will chose the 8 requests from
> its
> > queue that are contiguous, and so it will be writing around 256
> MiB,
> > which will take 2-3 seconds.  If it then needs to spend between 1
> and
> > 10 ms seeking to another location of the disk, before it writes
> the
> > next 256 MiB, the worst case overhead of that seek is 10ms / 2s,
> or
> > 0.5%.  That may very well be within your measurements' error bars.
> 
> Looks you assume that disk seeking just happens once when writing
> around
> 256MB. This assumption may not be true, given all data can be in
> page
> cache before writing. So when two tasks are submitting IOs
> concurrently,
> IOs from each single task is sequential, and NCQ may order the
> current batch
> submitted from the two streams. However disk seeking may still be
> needed
> for the next batch handled by NCQ.
> 
> > And of course, note that in real life, we are very *often* writing
> to
> > multiple files in parallel, for example, during a "make -j16"
> while
> > building the kernel.  Writing a single large file is certainly
> > something people do (but even there people who are burning a 4G
> DVD
> > rip are often browsing the web while they are waiting for it to
> > complete, and the browser will be writing cache files, etc.).  So
> > whether or not this is something where we should be stressing over
> > this specific workload is going to be quite debateable.
> 

Hi,
  is there any update on this? Sorry if I am making noise, but I would
like to help to improve the kernel (or fix it) if I can help.
Otherwise, please let me know how to consider this case,

Thanks, and bye
Andrea


  reply index

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <307581a490b610c3025ee80f79a465a89d68ed19.camel@unipv.it>
2019-08-20 17:13 ` Alan Stern
2019-08-23 10:39   ` Andrea Vai
2019-08-23 20:42     ` Alan Stern
2019-08-26  6:09       ` Andrea Vai
2019-08-26 16:33         ` Alan Stern
2019-09-18 15:25           ` Andrea Vai
2019-09-18 16:30             ` Alan Stern
2019-09-19  7:33               ` Andrea Vai
2019-09-19 17:54                 ` Alan Stern
2019-09-20  7:25                   ` Andrea Vai
2019-09-20  7:44                     ` Greg KH
2019-09-19  8:26               ` Damien Le Moal
2019-09-19  8:55                 ` Ming Lei
2019-09-19  9:09                   ` Damien Le Moal
2019-09-19  9:21                     ` Ming Lei
2019-09-19 14:01                 ` Alan Stern
2019-09-19 14:14                   ` Damien Le Moal
2019-09-20  7:03                     ` Andrea Vai
2019-09-25 19:30                       ` Alan Stern
2019-09-25 19:36                         ` Jens Axboe
2019-09-27 15:47                           ` Andrea Vai
2019-11-04 16:00                             ` Andrea Vai
2019-11-04 18:20                               ` Alan Stern
2019-11-05 11:48                                 ` Andrea Vai
2019-11-05 18:31                                   ` Alan Stern
2019-11-05 23:29                                     ` Jens Axboe
2019-11-06 16:03                                       ` Alan Stern
2019-11-06 22:13                                         ` Damien Le Moal
2019-11-07  7:04                                           ` Andrea Vai
2019-11-07  7:54                                             ` Damien Le Moal
2019-11-07 18:59                                               ` Andrea Vai
2019-11-08  8:42                                                 ` Damien Le Moal
2019-11-08 14:33                                                   ` Jens Axboe
2019-11-11 10:46                                                     ` Andrea Vai
2019-11-09 10:09                                                   ` Ming Lei
2019-11-09 22:28                                                 ` Ming Lei
2019-11-11 10:50                                                   ` Andrea Vai
2019-11-11 11:05                                                     ` Ming Lei
2019-11-11 11:13                                                       ` Andrea Vai
2019-11-22 19:16                                                   ` Andrea Vai
2019-11-23  7:28                                                     ` Ming Lei
2019-11-23 15:44                                                       ` Andrea Vai
2019-11-25  3:54                                                         ` Ming Lei
2019-11-25 10:11                                                           ` Andrea Vai
2019-11-25 10:29                                                             ` Ming Lei
2019-11-25 14:58                                                               ` Andrea Vai
2019-11-25 15:15                                                                 ` Ming Lei
2019-11-25 18:51                                                                   ` Andrea Vai
2019-11-26  2:32                                                                     ` Ming Lei
2019-11-26  7:46                                                                       ` Andrea Vai
2019-11-26  9:15                                                                         ` Ming Lei
2019-11-26 10:24                                                                           ` Ming Lei
2019-11-26 11:14                                                                           ` Andrea Vai
2019-11-27  2:05                                                                             ` Ming Lei
2019-11-27  9:39                                                                               ` Andrea Vai
2019-11-27 13:08                                                                                 ` Ming Lei
2019-11-27 15:01                                                                                   ` Andrea Vai
2019-11-27  0:21                                                                         ` Finn Thain
2019-11-27  8:14                                                                           ` AW: " Schmid, Carsten
2019-11-27 21:49                                                                             ` Finn Thain
2019-11-28  7:46                                                                             ` Andrea Vai
2019-11-28  8:12                                                                               ` AW: " Schmid, Carsten
2019-11-28 11:40                                                                                 ` Andrea Vai
2019-11-28 17:39                                                                                 ` Alan Stern
2019-11-28  9:17                                                                               ` Ming Lei
2019-11-28 17:34                                                                                 ` Andrea Vai
2019-11-29  0:57                                                                                   ` Ming Lei
2019-11-29  2:35                                                                                     ` Ming Lei
2019-11-29 14:41                                                                                       ` Andrea Vai
2019-12-03  2:23                                                                                         ` Ming Lei
2019-12-10  7:35                                                                                           ` Andrea Vai
2019-12-10  8:05                                                                                             ` Ming Lei
2019-12-11  2:41                                                                                               ` Theodore Y. Ts'o
2019-12-11  4:00                                                                                                 ` Ming Lei
2019-12-11 16:07                                                                                                   ` Theodore Y. Ts'o
2019-12-11 21:33                                                                                                     ` Ming Lei
2019-12-12  7:34                                                                                                       ` Andrea Vai
2019-12-18  8:25                                                                                                       ` Andrea Vai
2019-12-18  9:48                                                                                                         ` Ming Lei
     [not found]                                                                                                           ` <b1b6a0e9d690ecd9432025acd2db4ac09f834040.camel@unipv.it>
2019-12-23 13:08                                                                                                             ` Ming Lei
2019-12-23 14:02                                                                                                               ` Andrea Vai
2019-12-24  1:32                                                                                                                 ` Ming Lei
2019-12-24  8:04                                                                                                                   ` Andrea Vai
2019-12-24  8:47                                                                                                                     ` Ming Lei
2019-12-23 16:26                                                                                                               ` Theodore Y. Ts'o
2019-12-23 16:29                                                                                                                 ` Andrea Vai
2019-12-23 17:22                                                                                                                   ` Theodore Y. Ts'o
2019-12-23 18:45                                                                                                                     ` Andrea Vai
2019-12-23 19:53                                                                                                                       ` Theodore Y. Ts'o
2019-12-24  1:27                                                                                                                         ` Ming Lei
2019-12-24  6:49                                                                                                                           ` Andrea Vai
2019-12-24  8:51                                                                                                                           ` Andrea Vai
2019-12-24  9:35                                                                                                                             ` Ming Lei
2019-12-25  5:17                                                                                                                           ` Theodore Y. Ts'o
2019-12-26  2:27                                                                                                                             ` Ming Lei
2019-12-26  3:30                                                                                                                               ` Theodore Y. Ts'o
2019-12-26  8:37                                                                                                                                 ` Ming Lei
2020-01-07  7:51                                                                                                                                   ` Andrea Vai [this message]
     [not found]                                                                                                                                 ` <20200101074310.10904-1-hdanton@sina.com>
2020-01-01 13:53                                                                                                                                   ` slow IO on USB media Ming Lei
2019-11-29 11:44                                                                                     ` AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6 Bernd Schubert
2019-12-02  7:01                                                                                       ` Andrea Vai
2019-11-28 17:10                                                                           ` Andrea Vai

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