Re: Performance of ext4
From: Holger Kiehl
Date: Wed Jun 11 2008 - 16:22:11 EST
On Wed, 11 Jun 2008, Theodore Tso wrote:
On Wed, Jun 11, 2008 at 08:02:32AM +0000, Holger Kiehl wrote:
Doing some performance test between ext3 and ext4 I noticed that ext4
is not much faster or in some cases slower then ext3. Two years ago when
I tested ext4 it was a lot faster then ext3 (see my mail:
http://lkml.org/lkml/2006/6/6/65). Doing some simple tests with bonnie++
I got the following results:
Hi Holger,
You didn't say exactly which version of the kernel/ext4 you were
testing, but a recent change which we made to ext4, but which hasn't
been made to ext3 yet is that barrier support has been enabled to
improve filesystem safety; unfortunately this does imply with it a
slight performance slowdown, which would be more pronounced on
benchmarks with small filesystems.
I think you mean 'small files'? The test where done with a plain 2.6.25.4,
does that already have barriers enabled? While I did some test I hit this bug:
Jun 11 19:27:39 helena kernel: EXT4-fs: mballoc: 62053 blocks 62053 reqs (0 success)
Jun 11 19:27:39 helena kernel: EXT4-fs: mballoc: 62053 extents scanned, 14086 goal hits, 47967 2^N hits, 0 breaks, 0 lost
Jun 11 19:27:39 helena kernel: EXT4-fs: mballoc: 561 generated and it took 4080175
Jun 11 19:27:39 helena kernel: EXT4-fs: mballoc: 20889593 preallocated, 2761463 discarded
Jun 11 19:28:05 helena kernel: kjournald2 starting. Commit interval 15 seconds
Jun 11 19:28:05 helena kernel: EXT4 FS on md7, internal journal
Jun 11 19:28:05 helena kernel: EXT4-fs: mounted filesystem with ordered data mode.
Jun 11 19:28:05 helena kernel: EXT4-fs: file extents enabled
Jun 11 19:28:05 helena kernel: EXT4-fs: mballoc enabled
Jun 11 19:28:50 helena kernel: JBD: barrier-based sync failed on md7 - disabling barriers
Jun 11 19:28:50 helena kernel: ------------[ cut here ]------------
Jun 11 19:28:50 helena kernel: kernel BUG at fs/buffer.c:2879!
Jun 11 19:28:50 helena kernel: invalid opcode: 0000 [1] SMP
Jun 11 19:28:50 helena kernel: CPU 0
Jun 11 19:28:50 helena kernel: Modules linked in: w83627hf lm85 hwmon_vid bonding ipt_REJECT xt_tcpudp nf_conntrack_ipv4 xt_state nf_conntrack iptable_filter ip_tables x_tables binfmt_misc floppy i2c_amd756 k8temp i2c_core sg ohci_hcd button usbcore
Jun 11 19:28:50 helena kernel: Pid: 26731, comm: kjournald2 Not tainted 2.6.25.4 #12
Jun 11 19:28:50 helena kernel: RIP: 0010:[submit_bh+16/253] [submit_bh+16/253] submit_bh+0x10/0xfd
Jun 11 19:28:50 helena kernel: RSP: 0018:ffff8101775fdce0 EFLAGS: 00010246
Jun 11 19:28:50 helena kernel: RAX: 000000000000a02b RBX: ffff81005a182d90 RCX: ffff81027d7c7e60
Jun 11 19:28:50 helena kernel: RDX: 0000000100000000 RSI: ffff81005a182d90 RDI: 0000000000000001
Jun 11 19:28:50 helena kernel: RBP: 0000000000000001 R08: ffffffff8054cdd0 R09: 00000000fffff7e8
Jun 11 19:28:50 helena kernel: R10: ffff810001009940 R11: 0000000000000046 R12: ffff8101972ee000
Jun 11 19:28:50 helena kernel: R13: ffff81007ee79d00 R14: ffff8101775fde48 R15: 00000000fffffffb
Jun 11 19:28:50 helena kernel: FS: 00007f31d2ed67a0(0000) GS:ffffffff8057c000(0000) knlGS:0000000000000000
Jun 11 19:28:50 helena kernel: CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
Jun 11 19:28:50 helena kernel: CR2: 00007f13a584a000 CR3: 000000027ee35000 CR4: 00000000000006e0
Jun 11 19:28:50 helena kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Jun 11 19:28:50 helena kernel: DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Jun 11 19:28:50 helena kernel: Process kjournald2 (pid: 26731, threadinfo ffff8101775fc000, task ffff81013773d680)
Jun 11 19:28:50 helena kernel: Stack: ffff8101972ee024 ffff81005a182d90 ffff8101972ee000 ffffffff802f5f96
Jun 11 19:28:50 helena kernel: ffff81000037646d ffffffff8023c8cf 0000000000000003 0000000000000287
Jun 11 19:28:50 helena kernel: ffff81005a182850 ffff810075df7240 0000000000000000 ffff8101972ee000
Jun 11 19:28:50 helena kernel: Call Trace:
Jun 11 19:28:50 helena kernel: [journal_submit_commit_record+315/331] ? journal_submit_commit_record+0x13b/0x14b
Jun 11 19:28:50 helena kernel: [bit_waitqueue+16/163] ? bit_waitqueue+0x10/0xa3
Jun 11 19:28:50 helena kernel: [jbd2_journal_commit_transaction+2811/3994] ? jbd2_journal_commit_transaction+0xafb/0xf9a
Jun 11 19:28:50 helena kernel: [lock_timer_base+38/76] ? lock_timer_base+0x26/0x4c
Jun 11 19:28:50 helena kernel: [kjournald2+223/514] ? kjournald2+0xdf/0x202
Jun 11 19:28:50 helena kernel: [autoremove_wake_function+0/46] ? autoremove_wake_function+0x0/0x2e
Jun 11 19:28:50 helena kernel: [kjournald2+0/514] ? kjournald2+0x0/0x202
Jun 11 19:28:50 helena kernel: [kthread+71/115] ? kthread+0x47/0x73
Jun 11 19:28:50 helena kernel: [child_rip+10/18] ? child_rip+0xa/0x12
Jun 11 19:28:50 helena kernel: [kthread+0/115] ? kthread+0x0/0x73
Jun 11 19:28:50 helena kernel: [child_rip+0/18] ? child_rip+0x0/0x12
Jun 11 19:28:50 helena kernel:
Jun 11 19:28:50 helena kernel:
Jun 11 19:28:50 helena kernel: Code: 5f 08 e8 14 fb ff ff 48 3b 5c 24 08 48 89 df eb eb 41 5b 5b 5b 89 e8 5d 41 5c c3 41 54 55 89 fd 53 48 8b 06 48 89 f3 a8 04 75 04 <0f> 0b eb fe a8 20 75 04 0f 0b eb fe 48 83 7e 38 00 75 04 0f 0b
Jun 11 19:28:50 helena kernel: RIP [submit_bh+16/253] submit_bh+0x10/0xfd
Jun 11 19:28:50 helena kernel: RSP <ffff8101775fdce0>
Jun 11 19:28:50 helena kernel: ---[ end trace 5b73613cd770052b ]---
That happened when the filesystem (mounted with barrier=0) was unmounted
and then mounted with barrier=1.
So when you mount the filesystem
for ext3 and ext4 for benchmarking purposes, you should consistently
use a mount options of barrier=1 or barrier=0. With ext4, you can use
the mount option "barrier=1,journal_async_commit" which should
ameliorate part of the performance decrease. The reason why it is not
yet the default is it requires support from e2fsprogs that has not
been released except in development git branches; but as long as you
don't require running e2fsck on uncleanly shutdown systems (probably
not necessary if you are just benchmarking), you can use
journal_async_commit in good health.
Another change which might help out the bonnie benchmark, but which
again requires the latest version of e2fsprogs is to create the
filesystem with flex_bg filesystem feature. In fact, for
convenience's sake, if you are using the latest development version of
e2fsprogs, you can just use the command "mke2fs -t ext4dev /dev/hdXX"
and it will set up the filesystem with the correct filesystem features
for ext4. (The "ext4dev" sets the test_fs feature, and is basically
there so it's clear we are still trying to finish up ext4 support.)
Thank you for the detailed suggestions. I will try those and post the
results as soon as I have them.
Holger
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