Hi David, Sorry if all what follows is misguided nonsense. I'm eager to learn... David Teigland <teigland@xxxxxxxxxx> writes: > The new code has much better caching in the dlm which will benefit flocks, > look at these flock numbers I sent before: [...] > > This is testing raw flock performance. The dlm locks for normal file > operations should be cached and locally mastered also, so I'm not sure > what's causing the long times. Make sure that drop_count is zero again, > now it's in sysfs: > echo 0 > /sys/fs/gfs/<foo>:<bar>/lock_module/drop_count > > Also, mount debugfs so we can check some stuff later: > mount -t debugfs none /sys/kernel/debug > > Then run some tests: > - mount on nodeA > - run the test on nodeA > - count locks on nodeA > (cat /sys/kernel/debug/dlm/<bar> | grep Master | wc -l) > - mount on nodeB (don't do anything on this node) > - run the test again on nodeA > - count locks on nodeA and nodeB (see above) > - mount on nodeC (don't do anything on nodes B or C) > - run the test again on nodeA > - count locks on nodes A, B and C (see above) > > We're basically trying to produce the best-case performance from one node, > nodeA. That means making sure that nodeA is mastering all locks and doing > maximum caching. That's why it's important that we not do anything at all > that accesses the fs on nodes B or C, or do any extra mounts/unmounts. I made all the above tests and composed the reply a long time ago, but now, getting back to it after that long time, I decided to satisfy your curiosity, behold... > Plocks will be much slower and are probably not interesting to test, but > I'm curious if you added the "-l0" option to gfs_controld? That option > turns off the code that intentionally limits the rate of plocks. See the > old results again: [...] Now, that switch makes ALL the difference. With a single node switched on, I get results like this (with abbreviated strace -c output appended): without -l0: filecount=500 iteration=0 elapsed time=10.444446 s iteration=1 elapsed time=9.693618 s iteration=2 elapsed time=10.520073 s iteration=3 elapsed time=10.521504 s iteration=4 elapsed time=10.520183 s total elapsed time=51.699824 s Process 5265 detached % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 83.27 0.048525 6 7551 read 6.73 0.003923 2 2502 fcntl64 4.47 0.002606 1 2528 close 3.09 0.001801 1 2551 23 open 0.74 0.000432 0 2507 write 0.71 0.000415 0 5033 mmap2 0.41 0.000237 0 12528 3 _llseek 0.31 0.000178 0 5001 munmap 0.18 0.000107 0 5015 fstat64 0.08 0.000049 0 2506 gettimeofday 0.00 0.000000 0 16 14 ioctl 0.00 0.000000 0 202 182 stat64 ------ ----------- ----------- --------- --------- ---------------- 100.00 0.058273 47974 229 total with -l0: filecount=500 iteration=0 elapsed time=5.966146 s iteration=1 elapsed time=0.582058 s iteration=2 elapsed time=0.528272 s iteration=3 elapsed time=0.936438 s iteration=4 elapsed time=0.528147 s total elapsed time=8.541061 s Process 10030 detached % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 57.17 0.016527 2 7551 read 21.49 0.006213 2 2528 close 8.16 0.002358 1 2502 fcntl64 6.59 0.001904 1 2551 23 open 2.21 0.000638 0 2507 write 1.46 0.000421 0 5033 mmap2 0.86 0.000249 249 1 execve 0.73 0.000212 0 5001 munmap 0.65 0.000187 0 12528 3 _llseek 0.57 0.000165 0 5015 fstat64 0.12 0.000034 0 2506 gettimeofday 0.00 0.000000 0 16 14 ioctl 0.00 0.000000 0 202 182 stat64 ------ ----------- ----------- --------- --------- ---------------- 100.00 0.028908 47974 229 total Looks like the bottleneck isn't the explicit locking (be it plock or flock), but something else, like the built-in GFS locking. Similar dramatic speedup can be achieved (with a single node switched on, again), by the lockproto=lock_nolock mount option, even if used together with ignore_local_fs. It I understand it right, this combination leaves the cluster-wide [pf]locks alone, just eliminates the GFS internal locking, which guards the internal consistency of the file system (please correct me if I'm wrong). What's strange, is that gfs_controld -l0 seems like a perfectly safe invocation (what's the catch, ie. why was the artifical limit introduced?), still it achieves almost the same speedup like using lock_nolock, which would be a disaster with more than one node mounting the fs. (Also this trick scales pretty well to 4000 files.) Again, the above tests were done with a single node switched on, and I'm not sure whether the results carry over to the real cluster setup, will test is soon. I didn't touch drop_count either, everything was left as default, except for the mount options and the -l option. Also, I can send the results of the scenario suggested by you, if it's still relevant. In short: the locks are always mastered on node A only, but the performance is poor nevertheless. -- Regards, Feri. -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
