fsync slowness + XFS -- Regd.

fsync slowness + XFS -- Regd.

[Jeno P]

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Dear folks,

Hoping all are doing good.

*Issue*:- Slowness in fsync()

*System details*:-

OS:- CentOS Linux *7.4*
Linux Kernel:- *3.10.0-514 x86-64*
File system:- *XFS*


One of my module *(C/C++)* is writing to log files and periodically flushes
it using *fsync()*. Even for small amount of data, *fsync* is taking more
time *(>15 seconds)* than expected. Consequently, the main process was
timed-out and got killed. Confirmed the slowness through strace. Observed
the same behavior with *fsync* alternatives - *fdatasync & syncfs *as well
*. *The odd thing is even with very very minimal disk I/O, same issue is
happening. Did anybody face the issue ?


I saw in this forum that performance improvements with respect to *fysnc* has
already been made in file systems *ext2, ext3, brtfs* and *f2fs *in latest
Kernels. I saw a similar improvement in quite old Kernel *(2.6.34)*  for
*XFS*. But, I didn't see any such improvements *(for XFS)* in *newer
Kernels*. Should I need to downgrade my Kernel and observe the issue ? I
fear that downgrading may lead to other performance issues. Is there a
patch being planned in latest Kernel for CentOS ?


Looking forward to hear back from you all.

Thanks,
Jeno

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Re: fsync slowness + XFS -- Regd.

[Valdis Klētnieks]

On Tue, 19 Mar 2019 07:40:29 +0530, Jeno P said:

> One of my module *(C/C++)* is writing to log files and periodically flushes
> it using *fsync()*. Even for small amount of data, *fsync* is taking more
> time *(>15 seconds)* than expected.

Is it possible that some other process is applying a file lock to the log file?
Any signs of I/O errors? 15 seconds is the sort of delay you might see on a
RAID controller with one dead or partially dead disk throwing timeouts...


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Re: fsync slowness + XFS -- Regd.

[Alex Painemilla]

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Another possibility could be that the disk is in sleep mode and it needs to
wake up (A feature enabled on most green drives)

On Tue, Mar 19, 2019 at 5:03 PM Valdis Klētnieks <valdis.kletnieks@vt.edu>
wrote:

> On Tue, 19 Mar 2019 07:40:29 +0530, Jeno P said:
>
> > One of my module *(C/C++)* is writing to log files and periodically
> flushes
> > it using *fsync()*. Even for small amount of data, *fsync* is taking more
> > time *(>15 seconds)* than expected.
>
> Is it possible that some other process is applying a file lock to the log
> file?
> Any signs of I/O errors? 15 seconds is the sort of delay you might see on a
> RAID controller with one dead or partially dead disk throwing timeouts...
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies@kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

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