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2abd9e1c58
Every time we add free space to the free space tree or we remove free
space from the free space tree, we do a lookup for the block group's free
space info item in the free space tree. This takes time, navigating the
btree and we may block either on IO when reading extent buffers from disk
or on extent buffer lock contention due to concurrency.
Instead of doing this lookup every time, cache the result in the block
structure and use it after the first lookup. This adds two boolean members
to the block group structure but doesn't increase the structure's size.
The following script that runs fs_mark was used to measure the time spent
on run_delayed_tree_ref(), since down that call chain we have calls to
add and remove free space to/from the free space tree (calls to
btrfs_add_to_free_space_tree() and btrfs_remove_from_free_space_tree()):
$ cat test.sh
#!/bin/bash
DEV=/dev/nullb0
MNT=/mnt
FILES=100000
THREADS=$(nproc --all)
echo "performance" | \
tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
mount -o ssd $DEV $MNT
OPTS="-S 0 -L 5 -n $FILES -s 0 -t $THREADS -k"
for ((i = 1; i <= $THREADS; i++)); do
OPTS="$OPTS -d $MNT/d$i"
done
fs_mark $OPTS
umount $MNT
This is a heavy metadata test as it's exercising only file creation, so a
lot of allocations of metadata extents, creating delayed refs for adding
new metadata extents and dropping existing ones due to COW. The results
of the times it took to execute run_delayed_tree_ref(), in nanoseconds,
are the following.
Before this change:
Range: 1868.000 - 6482857.000; Mean: 10231.430; Median: 7005.000; Stddev: 27993.173
Percentiles: 90th: 13342.000; 95th: 23279.000; 99th: 82448.000
1868.000 - 4222.038: 270696 ############
4222.038 - 9541.029: 1201327 #####################################################
9541.029 - 21559.383: 385436 #################
21559.383 - 48715.063: 64942 ###
48715.063 - 110073.800: 31454 #
110073.800 - 248714.944: 8218 |
248714.944 - 561977.042: 1030 |
561977.042 - 1269798.254: 295 |
1269798.254 - 2869132.711: 116 |
2869132.711 - 6482857.000: 28 |
After this change:
Range: 1554.000 - 4557014.000; Mean: 9168.164; Median: 6391.000; Stddev: 21467.060
Percentiles: 90th: 12478.000; 95th: 20964.000; 99th: 72234.000
1554.000 - 3453.820: 219004 ############
3453.820 - 7674.743: 980645 #####################################################
7674.743 - 17052.574: 552486 ##############################
17052.574 - 37887.762: 68558 ####
37887.762 - 84178.322: 31557 ##
84178.322 - 187024.331: 12102 #
187024.331 - 415522.355: 1364 |
415522.355 - 923187.626: 256 |
923187.626 - 2051092.468: 125 |
2051092.468 - 4557014.000: 21 |
Approximate improvement in the first four buckets is about 20%.
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.