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Date: Wed, 14 Nov 2012 16:57:39 +0100
From: Martin Steigerwald <Martin@...htvoll.de>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, Kim Jaegeuk <jaegeuk.kim@...il.com>,
Jaegeuk Kim <jaegeuk.kim@...sung.com>,
linux-fsdevel@...r.kernel.org, gregkh@...uxfoundation.org,
viro@...iv.linux.org.uk, tytso@....edu, chur.lee@...sung.com,
cm224.lee@...sung.com, jooyoung.hwang@...sung.com
Subject: Re: [PATCH 00/16 v3] f2fs: introduce flash-friendly file system
Am Montag, 12. November 2012 schrieb Arnd Bergmann:
> On Monday 12 November 2012, Martin Steigerwald wrote:
> > Am Samstag, 10. November 2012 schrieb Arnd Bergmann:
>
> > > I would also recommend using flashbench to find out the optimum parameters
> > > for your device. You can download it from
> > > git://git.linaro.org/people/arnd/flashbench.git
> > > In the long run, we should automate those tests and make them part of
> > > mkfs.f2fs, but for now, try to find out the erase block size and the number
> > > of concurrently used erase blocks on your device using a timing attack
> > > in flashbench. The README file in there explains how to interpret the
> > > results from "./flashbench -a /dev/sdb --blocksize=1024" to guess
> > > the erase block size, although that sometimes doesn't work.
> >
> > Why do I use a blocksize of 1024 if the kernel reports me 512 byte blocks?
>
> The blocksize you pass here is the size of writes that flashbench sends to the
> kernel. Because of the algorithm used by flashbench, two hardware blocks
> is the smallest size you can use here, and larger block tend to be less reliable
> for this test case. I should probably change the default.
>
> > [ 3112.144086] scsi9 : usb-storage 1-1.1:1.0
> > [ 3113.145968] scsi 9:0:0:0: Direct-Access TinyDisk 2007-05-12 0.00 PQ: 0 ANSI: 2
> > [ 3113.146476] sd 9:0:0:0: Attached scsi generic sg2 type 0
> > [ 3113.147935] sd 9:0:0:0: [sdb] 4095999 512-byte logical blocks: (2.09 GB/1.95 GiB)
> > [ 3113.148935] sd 9:0:0:0: [sdb] Write Protect is off
> >
> >
> > And how do reads give information about erase block size? Wouldn´t writes me
> > more conclusive for that? (Having to erase one versus two erase blocks?)
>
> The --open-au tests can be more reliable, but also take more time and are
> harder to understand. Using this test is faster and often gives an easy
> answer even without destroying data on the device.
>
>
> > Hmmm, I get very varying results here with said USB stick:
> >
> > merkaba:~> /tmp/flashbench -a /dev/sdb
> > align 536870912 pre 1.1ms on 1.1ms post 1.08ms diff 13µs
> > align 268435456 pre 1.2ms on 1.19ms post 1.16ms diff 11.6µs
> > align 134217728 pre 1.12ms on 1.14ms post 1.15ms diff 9.51µs
> > align 67108864 pre 1.12ms on 1.15ms post 1.12ms diff 29.9µs
> > align 33554432 pre 1.11ms on 1.17ms post 1.13ms diff 49µs
> > align 16777216 pre 1.14ms on 1.16ms post 1.15ms diff 22.4µs
> > align 8388608 pre 1.12ms on 1.09ms post 1.06ms diff -2053ns
> > align 4194304 pre 1.13ms on 1.16ms post 1.14ms diff 21.7µs
> > align 2097152 pre 1.11ms on 1.08ms post 1.1ms diff -18488n
> > align 1048576 pre 1.11ms on 1.11ms post 1.11ms diff -2461ns
> > align 524288 pre 1.15ms on 1.17ms post 1.1ms diff 45.4µs
> > align 262144 pre 1.11ms on 1.13ms post 1.13ms diff 12µs
> > align 131072 pre 1.1ms on 1.09ms post 1.16ms diff -38025n
> > align 65536 pre 1.09ms on 1.08ms post 1.11ms diff -21353n
> > align 32768 pre 1.1ms on 1.08ms post 1.11ms diff -23854n
> > merkaba:~> /tmp/flashbench -a /dev/sdb
> > align 536870912 pre 1.11ms on 1.13ms post 1.13ms diff 10.6µs
> > align 268435456 pre 1.12ms on 1.2ms post 1.17ms diff 61.4µs
> > align 134217728 pre 1.14ms on 1.19ms post 1.15ms diff 46.8µs
> > align 67108864 pre 1.08ms on 1.15ms post 1.08ms diff 63.8µs
> > align 33554432 pre 1.09ms on 1.08ms post 1.09ms diff -4761ns
> > align 16777216 pre 1.12ms on 1.14ms post 1.07ms diff 41.4µs
> > align 8388608 pre 1.1ms on 1.1ms post 1.09ms diff 7.48µs
> > align 4194304 pre 1.08ms on 1.1ms post 1.1ms diff 10.1µs
> > align 2097152 pre 1.1ms on 1.11ms post 1.1ms diff 16µs
> > align 1048576 pre 1.09ms on 1.1ms post 1.07ms diff 15.5µs
> > align 524288 pre 1.12ms on 1.12ms post 1.1ms diff 11µs
> > align 262144 pre 1.13ms on 1.13ms post 1.1ms diff 21.6µs
> > align 131072 pre 1.11ms on 1.13ms post 1.12ms diff 17.9µs
> > align 65536 pre 1.07ms on 1.1ms post 1.1ms diff 11.6µs
> > align 32768 pre 1.09ms on 1.11ms post 1.13ms diff -5131ns
> > merkaba:~> /tmp/flashbench -a /dev/sdb
> > align 536870912 pre 1.2ms on 1.18ms post 1.21ms diff -27496n
> > align 268435456 pre 1.22ms on 1.21ms post 1.24ms diff -18972n
> > align 134217728 pre 1.15ms on 1.19ms post 1.14ms diff 42.5µs
> > align 67108864 pre 1.08ms on 1.09ms post 1.08ms diff 5.29µs
> > align 33554432 pre 1.18ms on 1.19ms post 1.18ms diff 9.25µs
> > align 16777216 pre 1.18ms on 1.22ms post 1.17ms diff 48.6µs
> > align 8388608 pre 1.14ms on 1.17ms post 1.19ms diff 4.36µs
> > align 4194304 pre 1.16ms on 1.2ms post 1.11ms diff 65.8µs
> > align 2097152 pre 1.13ms on 1.09ms post 1.12ms diff -37718n
> > align 1048576 pre 1.15ms on 1.2ms post 1.18ms diff 34.9µs
> > align 524288 pre 1.14ms on 1.19ms post 1.16ms diff 41.5µs
> > align 262144 pre 1.19ms on 1.12ms post 1.15ms diff -52725n
> > align 131072 pre 1.21ms on 1.11ms post 1.14ms diff -68522n
> > align 65536 pre 1.21ms on 1.13ms post 1.18ms diff -64248n
> > align 32768 pre 1.14ms on 1.25ms post 1.12ms diff 116µs
> >
> > Even when I apply the explaination of the README I do not seem to get a
> > clear picture of the stick erase block size.
> >
> > The values above seem to indicate to me: I don´t care about alignment at all.
>
> I think it's more a case of a device where reading does not easily reveal
> the erase block boundaries, because the variance between multiple reads
> is much higher than between different positions. You can try again using
> "--blocksize=1024 --count=100", which will increase the accuracy of the
> test.
>
> On the other hand, the device size of "4095999 512-byte logical blocks"
> is quite suspicious, because it's not an even number, where it should
> be a multiple of erase blocks. It is one less sector than 1000 2MB blocks
> (or 500 4MB blocks, for that matter), but it's not clear if that one
> block is missing at the start or at the end of the drive.
Just for this first flash drive, I think the erase block size if 4 MiB. The
-a count=100/100 tests did not show any obvious results, but the
--open-au ones did, I think. I would use two open allocation units (AUs).
Maybe also 1 AU, cause 64 KiB sized accesses are faster that way?
Well I tend to use one AU. So that device would be more suitable for FAT
than for BTRFS. Or more suitable for F2FS that is.
What do you think?
Only thing that seems to contradict this is the test with different
alignments below.
merkaba:~#254> /tmp/flashbench -a /dev/sdb --count=100
align 536870912 pre 1.06ms on 1.07ms post 1.04ms diff 14.6µs
align 268435456 pre 1.09ms on 1.1ms post 1.09ms diff 11.3µs
align 134217728 pre 1.09ms on 1.09ms post 1.1ms diff -87ns
align 67108864 pre 1.05ms on 1.06ms post 1.03ms diff 15.9µs
align 33554432 pre 1.06ms on 1.06ms post 1.03ms diff 18.7µs
align 16777216 pre 1.05ms on 1.05ms post 1.03ms diff 13.3µs
align 8388608 pre 1.05ms on 1.06ms post 1.04ms diff 9.03µs
align 4194304 pre 1.06ms on 1.06ms post 1.04ms diff 8.56µs
align 2097152 pre 1.06ms on 1.05ms post 1.05ms diff 2.02µs
align 1048576 pre 1.05ms on 1.04ms post 1.06ms diff -11524n
align 524288 pre 1.05ms on 1.05ms post 1.04ms diff 642ns
align 262144 pre 1.04ms on 1.04ms post 1.04ms diff -604ns
align 131072 pre 1.03ms on 1.04ms post 1.04ms diff 2.79µs
align 65536 pre 1.04ms on 1.05ms post 1.05ms diff 7.2µs
align 32768 pre 1.05ms on 1.05ms post 1.05ms diff -4475ns
merkaba:~> /tmp/flashbench -a /dev/sdb --count=1000
align 536870912 pre 1.03ms on 1.05ms post 1.02ms diff 20.3µs
align 268435456 pre 1.06ms on 1.05ms post 1.04ms diff 3.14µs
align 134217728 pre 1.07ms on 1.08ms post 1.05ms diff 16.1µs
align 67108864 pre 1.03ms on 1.03ms post 1.02ms diff 11µs
align 33554432 pre 1.02ms on 1.03ms post 1.01ms diff 10.3µs
align 16777216 pre 1.03ms on 1.04ms post 1.02ms diff 9.68µs
align 8388608 pre 1.04ms on 1.03ms post 1.02ms diff 6.45µs
align 4194304 pre 1.03ms on 1.04ms post 1.02ms diff 9.12µs
align 2097152 pre 1.04ms on 1.04ms post 1.02ms diff 15.4µs
align 1048576 pre 1.03ms on 1.03ms post 1.03ms diff -1590ns
align 524288 pre 1.03ms on 1.03ms post 1.03ms diff -835ns
align 262144 pre 1.04ms on 1.04ms post 1.03ms diff 1.25µs
align 131072 pre 1.03ms on 1.03ms post 1.03ms diff -3477ns
align 65536 pre 1.03ms on 1.03ms post 1.03ms diff 191ns
align 32768 pre 1.03ms on 1.04ms post 1.03ms diff 4.06µs
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[16*1024*1024]
16MiB 15M/s
8MiB 3.44M/s
4MiB 13.9M/s
2MiB 13M/s
1MiB 15M/s
512KiB 3.3M/s
256KiB 6.55M/s
128KiB 4.17M/s
64KiB 13.5M/s
32KiB 2.15M/s
16KiB 1.83M/s
8KiB 1.25M/s
4KiB 731K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[8*1024*1024]
8MiB 14.6M/s
4MiB 8.11M/s
2MiB 12.5M/s
1MiB 15.1M/s
512KiB 3.29M/s
256KiB 6.54M/s
128KiB 4.16M/s
64KiB 13.4M/s
32KiB 2.14M/s
16KiB 1.81M/s
8KiB 1.23M/s
4KiB 722K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[4*1024*1024]
4MiB 14M/s
2MiB 13M/s
1MiB 15M/s
512KiB 3.26M/s
256KiB 6.57M/s
128KiB 4.2M/s
64KiB 13.3M/s
32KiB 2.13M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 724K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[2*1024*1024]
2MiB 13.1M/s
1MiB 15.2M/s
512KiB 3.22M/s
256KiB 6.57M/s
128KiB 4.2M/s
64KiB 13.3M/s
32KiB 2.11M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 725K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[2*1024*1024]
2MiB 13.1M/s
1MiB 14.9M/s
512KiB 3.21M/s
256KiB 6.61M/s
128KiB 4.19M/s
64KiB 13.3M/s
32KiB 2.11M/s
16KiB 1.82M/s
8KiB 1.23M/s
4KiB 726K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[1*1024*1024]
1MiB 14.9M/s
512KiB 3.12M/s
256KiB 6.64M/s
128KiB 4.2M/s
64KiB 13.4M/s
32KiB 2.07M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 725K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=2 --blocksize=4096 --erasesize=$[4*1024*1024]
4MiB 14.2M/s
2MiB 13.1M/s
1MiB 5.58M/s
512KiB 3.43M/s
256KiB 6.58M/s
128KiB 4.18M/s
64KiB 5.06M/s
32KiB 2.14M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 724K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=2 --blocksize=4096 --erasesize=$[16*1024*1024]
16MiB 5.68M/s
8MiB 4.3M/s
4MiB 14.2M/s
2MiB 13.1M/s
1MiB 5.6M/s
512KiB 3.35M/s
256KiB 6.61M/s
128KiB 4.19M/s
64KiB 5.07M/s
32KiB 2.16M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 726K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=3 --blocksize=4096 --erasesize=$[16*1024*1024]
16MiB 7.18M/s
8MiB 14.6M/s
4MiB 14.1M/s
2MiB 13M/s
1MiB 6.39M/s
512KiB 8.77M/s
256KiB 6.13M/s
128KiB 3.81M/s
64KiB 2.37M/s
32KiB 1.15M/s
16KiB 648K/s
8KiB 344K/s
4KiB 180K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[16*1024*1024]
16MiB 15.3M/s
8MiB 3.48M/s
4MiB 14.3M/s
2MiB 13.2M/s
1MiB 15.2M/s
512KiB 3.33M/s
256KiB 6.64M/s
128KiB 4.2M/s
64KiB 13.6M/s
32KiB 2.15M/s
16KiB 1.83M/s
8KiB 1.24M/s
4KiB 727K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=2 --blocksize=4096 --erasesize=$[16*1024*1024]
16MiB 5.72M/s
8MiB 4.33M/s
4MiB 14.3M/s
2MiB 13.3M/s
1MiB 5.66M/s
512KiB 3.38M/s
256KiB 6.68M/s
128KiB 4.24M/s
64KiB 5.12M/s
32KiB 2.17M/s
16KiB 1.83M/s
8KiB 1.24M/s
4KiB 729K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[4*1024*1024]
4MiB 14M/s
2MiB 13.3M/s
1MiB 15.3M/s
512KiB 3.29M/s
256KiB 6.68M/s
128KiB 4.22M/s
64KiB 13.7M/s
32KiB 2.15M/s
16KiB 1.83M/s
8KiB 1.24M/s
4KiB 729K/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=2 --blocksize=4096 --erasesize=$[4*1024*1024]
4MiB 14.1M/s
2MiB 13.1M/s
1MiB 5.62M/s
512KiB 3.43M/s
256KiB 6.63M/s
128KiB 4.2M/s
64KiB 5.11M/s
32KiB 2.15M/s
16KiB 1.82M/s
8KiB 1.24M/s
4KiB 727K/s
merkaba:~#130> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=$[16*1024*1024]
16MiB 15.2M/s
8MiB 3.46M/s
4MiB 14.2M/s
2MiB 13.1M/s
1MiB 15.1M/s
512KiB 3.31M/s
256KiB 6.59M/s
128KiB 4.19M/s
64KiB 13.5M/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=2 --blocksize=65536 --erasesize=$[16*1024*1024]
16MiB 5.68M/s
8MiB 4.31M/s
4MiB 14.2M/s
2MiB 13.2M/s
1MiB 5.62M/s
512KiB 3.36M/s
256KiB 6.63M/s
128KiB 4.21M/s
64KiB 5.09M/s
But then I tried with offset and get:
> > > With the correct guess, compare the performance you get using
> > >
> > > $ ERASESIZE=$[2*1024*1024] # replace with guess from flashbench -a
> > > $ ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=${ERASESIZE}
> > > $ ./flashbench /dev/sdb --open-au --open-au-nr=3 --blocksize=4096 --erasesize=${ERASESIZE}
> > > $ ./flashbench /dev/sdb --open-au --open-au-nr=5 --blocksize=4096 --erasesize=${ERASESIZE}
> > > $ ./flashbench /dev/sdb --open-au --open-au-nr=7 --blocksize=4096 --erasesize=${ERASESIZE}
> > > $ ./flashbench /dev/sdb --open-au --open-au-nr=13 --blocksize=4096 --erasesize=${ERASESIZE}
> >
> > I omit this for now, cause I am not yet sure about the correct guess.
>
> You can also try this test to find out the erase block size if the -a test fails.
> Start with the largest possible value you'd expect (16 MB for a modern and fast
> USB stick, less if it's older or smaller), and use --open-au-nr=1 to get a baseline:
>
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=4096 --erasesize=$[16*1024*1024]
>
> Every device should be able to handle this nicely with maximum throughput. The default is
> to start the test at 16 MB into the device to get out of the way of a potential FAT
> optimized area. You can change that offset to find where an erase block boundary is.
> Adding '--offset=[24*1024*1024]' will still be fast if the erase block size is 8 MB,
> but get slower and have more jitter if the size is actually 16 MB, because now we write
> a 16 MB section of the drive with an 8 MB misalignment. The next ones to try after that
> would be 20, 18, 17, 16.5, etc MB, to which will be slow for an 8,4, 2, an 1 MB erase
> block size, respectively. You can also reduce the --erasesize argument there and do
>
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=[16*1024*1024 --offset=[24*1024*1024]
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=[8*1024*1024 --offset=[20*1024*1024]
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=[4*1024*1024 --offset=[18*1024*1024]
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=[2*1024*1024 --offset=[17*1024*1024]
> ./flashbench /dev/sdb --open-au --open-au-nr=1 --blocksize=65536 --erasesize=[1*1024*1024 --offset=[33*512*1024]
>
> If you have the result from the other test to figure out the maximum value for
> '--open-au-nr=N', using that number here will make this test more reliable as well.
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --offset $[8*1024*1024] --erasesize=$[16*1024*1024]
16MiB 15.1M/s
8MiB 3.45M/s
4MiB 14M/s
2MiB 13.1M/s
1MiB 15.2M/s
512KiB 3.31M/s
256KiB 6.55M/s
128KiB 4.18M/s
64KiB 13.4M/s
32KiB 2.14M/s
16KiB 1.81M/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --offset $[1*1024*1024] --erasesize=$[4*1024*1024]
4MiB 14.1M/s
2MiB 13M/s
1MiB 14.9M/s
512KiB 3.25M/s
256KiB 6.56M/s
128KiB 4.16M/s
64KiB 13.4M/s
32KiB 2.13M/s
16KiB 1.81M/s
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --offset $[2*1024*1024] --erasesize=$[4*1024*1024]
4MiB 14M/s
2MiB 13M/s
1MiB 15.1M/s
512KiB 3.25M/s
256KiB 6.58M/s
128KiB 4.18M/s
64KiB 13.5M/s
32KiB 2.13M/s
16KiB 1.82M/s
So this does seem to me that the device quite likes 4 MiB sized, but doesn´t
care too much about their alignment?
merkaba:~> /tmp/flashbench /dev/sdb --open-au --open-au-nr=1 --offset $[78*1024] --erasesize=$[4*1024*1024]
4MiB 14.2M/s
2MiB 13.3M/s
1MiB 15.1M/s
512KiB 3.42M/s
256KiB 6.6M/s
128KiB 4.22M/s
64KiB 13.5M/s
32KiB 2.17M/s
16KiB 1.84M/s
Its seem thats a kinda special USB stick.
Thanks,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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