On 02/12/2013 08:43 AM, Anand Avati wrote:
On Mon, Feb 11, 2013 at 7:02 PM, Pranith Kumar K <pkara...@redhat.com
<mailto:pkara...@redhat.com>> wrote:
hi,
Problem:
When there are multiple fds writing to same file with eager-lock
enabled, the fd which acquires the eager-lock waits for
post-op-delay secs before doing the unlock. Because of this all
other fds opened on the file face extra delay when
performing writes. Eager-locking, post-op-delay need to be
disabled when there are multiple fds opened on the file.
Here is the profile info output for the case above:
Execute the following command on the mount point.
for n in `seq 1 50` ; do eval
"/home/pranithk/workspace/gerrit-repo/append2log.py ./ben.log
10000 0.001 &" ; done ; wait
%-latency Avg-latency Min-Latency Max-Latency No. of
calls Fop
--------- ----------- ----------- ----------- ------------
----
0.00 0.00 us 0.00 us 0.00 us 50 RELEASE
0.00 0.00 us 0.00 us 0.00 us 60 RELEASEDIR
0.00 55.00 us 55.00 us 55.00 us 1 GETXATTR
0.00 31.50 us 27.00 us 36.00 us 2 STATFS
0.00 41.00 us 29.00 us 53.00 us 2 ENTRYLK
0.00 198.00 us 198.00 us 198.00 us 1 CREATE
0.00 124.00 us 108.00 us 140.00 us 2 READDIR
0.00 27.04 us 17.00 us 95.00 us 49 OPEN
0.00 74.89 us 13.00 us 206.00 us 47 STAT
0.01 87.02 us 11.00 us 391.00 us 50 FLUSH
0.01 102.43 us 20.00 us 268.00 us 60 OPENDIR
0.02 344.27 us 22.00 us 940.00 us 44 WRITE
0.02 228.80 us 52.00 us 345.00 us 82 FXATTROP
0.03 199.89 us 19.00 us 404.00 us 120 READDIRP
0.05 91.41 us 23.00 us 832.00 us 421 LOOKUP
99.86 632698.45 us 17.00 us 1999724.00 us 126 FINODELK
Observe that most of the delay is in FINODELK fop.
Possible Solution:
With the patch: http://review.gluster.org/4468 we started
maintaining open-fd count in the inode. We need to implement xdata
based xattr retrieval in write-fop and get open-fd-count in write
fop. Remember the open-fd-count received from the write-fops and
maintain it in afr-fd-ctx. If the open-fd count is >1
post-op-delay is immediately disabled for that write fop. All
write-fops take into consideration this count to determine whether
to enable eager-lock, post-op-delay for that write fop.
Let me know if you foresee any issues with this approach.
https://bugzilla.redhat.com/show_bug.cgi?id=910217 is tracking
this issue.
Ideally you would want open-fd count to be retrieved in all fops, and
only when an eager lock has been acquired. Any fop callback's
xattr_rsp inspection should potentially wake up the sleeping
post-op-delay in that inode (and disable further eager locking
temporarily).
Avati
Avati,
Makes sense. Since it is in-memory virtual xattr retrieval,
performance should not be affected too much IMO. I will have to
implement and run perf-test to make sure of that. Other than that every
thing else is ok right?
I will start the implementation if no other issues are foreseen.
pranith.
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