which local FS supports concurrent direct IO write?

[Raghavendra D Prabhu]

Hi Zheng,

Interesting analysis. 

* On Sun, Jan 15, 2012 at 03:17:12PM -0500, Zheng Da <zhengda1936 at gmail.com> wrote:
>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. 
 From what I have heard it has supported it from sometime back. I 
think you may need to ask in xfs general ML about this.


>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.

 From what I saw in xfs_file_dio_aio_write code, it uses EXCL only 
if there is unaligned IO   or there are cached pages to be 
invalidated after shared lock is obtained *but* it demotes that 
lock to SHARED just before generic_file_direct_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
>> Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
>> www: wnohang.net




Regards,
-- 
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net
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