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SubjectRe: [RFC] ext4: Don't send extra barrier during fsync if there are no dirty pages.
On Tue, Aug 03, 2010 at 05:01:52AM -0400, Christoph Hellwig wrote:
> On Mon, Aug 02, 2010 at 05:09:39PM -0700, Darrick J. Wong wrote:
> > Well... on my fsync-happy workloads, this seems to cut the barrier count down
> > by about 20%, and speeds it up by about 20%.
>
> Care to share the test case for this? I'd be especially interesting on
> how it behaves with non-draining barriers / cache flushes in fsync.

Sure. When I run blktrace with the ffsb profile, I get these results:

barriers transactions/sec
16212 206
15625 201
10442 269
10870 266
15658 201

Without Jan's patch:
barriers transactions/sec
20855 177
20963 177
20340 174
20908 177

The two ~270 results are a little odd... if we ignore them, the net gain with
Jan's patch is about a 25% reduction in barriers issued and about a 15%
increase in tps. (If we don't, it's ~30% and ~30%, respectively.) That said,
I was running mkfs between runs, so it's possible that the disk layout could
have shifted a bit. If I turn off the fsync parts of the ffsb profile, the
barrier counts drop to about a couple every second or so, which means that
Jan's patch doesn't have much of an effect. But it does help if someone is
hammering on the filesystem with fsync.

The ffsb profile is attached below.

--D

-----------

time=300
alignio=1
directio=1

[filesystem0]
location=/mnt/
num_files=100000
num_dirs=1000

reuse=1
# File sizes range from 1kB to 1MB.
size_weight 1KB 10
size_weight 2KB 15
size_weight 4KB 16
size_weight 8KB 16
size_weight 16KB 15
size_weight 32KB 10
size_weight 64KB 8
size_weight 128KB 4
size_weight 256KB 3
size_weight 512KB 2
size_weight 1MB 1

create_blocksize=1048576
[end0]

[threadgroup0]
num_threads=64

readall_weight=4
create_fsync_weight=2
delete_weight=1

append_weight = 1
append_fsync_weight = 1
stat_weight = 1
create_weight = 1
writeall_weight = 1
writeall_fsync_weight = 1
open_close_weight = 1


write_size=64KB
write_blocksize=512KB

read_size=64KB
read_blocksize=512KB

[stats]
enable_stats=1
enable_range=1

msec_range 0.00 0.01
msec_range 0.01 0.02
msec_range 0.02 0.05
msec_range 0.05 0.10
msec_range 0.10 0.20
msec_range 0.20 0.50
msec_range 0.50 1.00
msec_range 1.00 2.00
msec_range 2.00 5.00
msec_range 5.00 10.00
msec_range 10.00 20.00
msec_range 20.00 50.00
msec_range 50.00 100.00
msec_range 100.00 200.00
msec_range 200.00 500.00
msec_range 500.00 1000.00
msec_range 1000.00 2000.00
msec_range 2000.00 5000.00
msec_range 5000.00 10000.00
[end]
[end0]


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