From: Dave Chinner <david@fromorbit.com>
To: linux-btrfs@vger.kernel.org
Subject: [4.8] btrfs heats my room with lock contention
Date: Thu, 4 Aug 2016 16:41:05 +1000 [thread overview]
Message-ID: <20160804064105.GT12670@dastard> (raw)
Simple test. 8GB pmem device on a 16p machine:
# mkfs.btrfs /dev/pmem1
# mount /dev/pmem1 /mnt/scratch
# dbench -t 60 -D /mnt/scratch 16
And heat your room with the warm air rising from your CPUs. Top
half of the btrfs profile looks like:
36.71% [kernel] [k] _raw_spin_unlock_irqrestore ¿
32.29% [kernel] [k] native_queued_spin_lock_slowpath ¿
5.14% [kernel] [k] queued_write_lock_slowpath ¿
2.46% [kernel] [k] _raw_spin_unlock_irq ¿
2.15% [kernel] [k] queued_read_lock_slowpath ¿
1.54% [kernel] [k] _find_next_bit.part.0 ¿
1.06% [kernel] [k] __crc32c_le ¿
0.82% [kernel] [k] btrfs_tree_lock ¿
0.79% [kernel] [k] steal_from_bitmap.part.29 ¿
0.70% [kernel] [k] __copy_user_nocache ¿
0.69% [kernel] [k] btrfs_tree_read_lock ¿
0.69% [kernel] [k] delay_tsc ¿
0.64% [kernel] [k] btrfs_set_lock_blocking_rw ¿
0.63% [kernel] [k] copy_user_generic_string ¿
0.51% [kernel] [k] do_raw_read_unlock ¿
0.48% [kernel] [k] do_raw_spin_lock ¿
0.47% [kernel] [k] do_raw_read_lock ¿
0.46% [kernel] [k] btrfs_clear_lock_blocking_rw ¿
0.44% [kernel] [k] do_raw_write_lock ¿
0.41% [kernel] [k] __do_softirq ¿
0.28% [kernel] [k] __memcpy ¿
0.24% [kernel] [k] map_private_extent_buffer ¿
0.23% [kernel] [k] find_next_zero_bit ¿
0.22% [kernel] [k] btrfs_tree_read_unlock ¿
Performance vs CPu usage is:
nprocs throughput cpu usage
1 440MB/s 50%
2 770MB/s 100%
4 880MB/s 250%
8 690MB/s 450%
16 280MB/s 950%
In comparision, at 8-16 threads ext4 is running at ~2600MB/s and
XFS is running at ~3800MB/s. Even if I throw 300-400 processes at
ext4 and XFS, they only drop to ~1500-2000MB/s as they hit internal
limits.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next reply other threads:[~2016-08-04 6:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-04 6:41 Dave Chinner [this message]
2016-08-04 14:28 ` [4.8] btrfs heats my room with lock contention Chris Mason
2016-08-05 3:01 ` Dave Chinner
2016-08-05 19:34 ` Chris Mason
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