which local FS supports concurrent direct IO write?

[Zheng Da]

Thanks. I was reading the code of kernel 3.0. XFS starts to support
concurrent direct IO since kernel 3.1.5.
But concurrent direct IO write still doesn't work well in kernel 3.2. I
wrote a test program that accesses a 4G file randomly (read and write), and
I ran it with 8 threads and the machine has 8 cores. It turns out that only
1 core is running. I'm pretty sure xfs_rw_ilock is locked
with XFS_IOLOCK_SHARED in xfs_file_dio_aio_write.

lockstat shows me that there is a lot of wait time in ip->i_lock. It seems
the lock is locked exclusively.
               &(&ip->i_lock)->mr_lock-W:         31568          36170
      0.24       20048.25     7589157.99         130154        3146848
      0.00         217.70     1238310.72
               &(&ip->i_lock)->mr_lock-R:         11251          11886
      0.24       20043.01     2895595.18          46671         526309
      0.00          63.80      264097.96
               -------------------------
                 &(&ip->i_lock)->mr_lock          36170
 [<ffffffffa03be122>] xfs_ilock+0xb2/0x110 [xfs]
                 &(&ip->i_lock)->mr_lock          11886
 [<ffffffffa03be15a>] xfs_ilock+0xea/0x110 [xfs]
               -------------------------
                 &(&ip->i_lock)->mr_lock          38555
 [<ffffffffa03be122>] xfs_ilock+0xb2/0x110 [xfs]
                 &(&ip->i_lock)->mr_lock           9501
 [<ffffffffa03be15a>] xfs_ilock+0xea/0x110 [xfs]

Then I used systemtap to instrument xfs_ilock and find there are at least 3
functions that lock ip->i_lock exclusively during write.
Is there any popular FS that supports concurrent direct IO well?

Thanks,
Da

On Sat, Jan 14, 2012 at 6:45 AM, Raghavendra D Prabhu <
raghu.prabhu13 at gmail.com> wrote:

> Hi Zheng,
>
>
> * On Fri, Jan 13, 2012 at 04:41:16PM -0500, Zheng Da <
> zhengda1936 at gmail.com> wrote:
>
>> Hello,
>>
>> I'm looking for a FS in Linux that supports concurrent direct IO write.
>> ext4 supports concurrent direct IO read if we mount it with
>> dioread_nolock,
>> but doesn't support concurrent writes. XFS doesn't support concurrent
>> direct IO at all. It locks the inode exclusive if it's direct IO. I tried
>> btrfs, and it seems it doesn't support concurrent direct IO either though
>> I
>> haven't looked into its code.
>> Is there a local FS that support concurrent direct IO write? It seems NFS
>> supports it (
>> http://kevinclosson.wordpress.**com/2011/08/12/file-systems-**
>> for-a-database-choose-one-**that-couples-direct-io-and-**
>> concurrent-io-whats-this-have-**to-do-with-nfs-harken-back-5-**
>> 2-years-to-find-out/<http://kevinclosson.wordpress.com/2011/08/12/file-systems-for-a-database-choose-one-that-couples-direct-io-and-concurrent-io-whats-this-have-to-do-with-nfs-harken-back-5-2-years-to-find-out/>
>> ),
>> but I'm looking for local FS.
>>
>> Thanks,
>> Da
>>
>
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>>
>
> XFS locks inode exclusive only if it is an unaligned Direct IO, which is
> apparently done to prevent race conditions -- refer to this
> http://oss.sgi.com/archives/**xfs/2011-01/msg00157.html<http://oss.sgi.com/archives/xfs/2011-01/msg00157.html>Also the behavior of Ext4 under dioread_nolock is supported by XFS by
> default and in a much better way. Also Ext4 is the only one which uses
> DIO_LOCKING while doing direct io.
>
>
>
> Regards,
> --
> Raghavendra Prabhu
> GPG Id : 0xD72BE977
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>
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