Asynchronous I/O
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From: Jeremy Allison on 7 Jun 2010 15:30 On Mon, Jun 07, 2010 at 07:07:46PM -0400, Andy Liebman wrote: > Hello, > > Is there any straightforward way to see whether Samba is using > "asynchronous i/o"? In other words, if you specify in smb.conf to use > aio for all transfers larger than 1 KB (pretty much everything), how can > you tell that aio is actually being used? Are there any counters in > Linux or in some samba logs that you can see incrementing over time? Currently aio on Linux is horribly broken due to a conservative glibc, which limits asynchronous requests to one outstanding one per file descriptor (which pretty much makes all io synchronous on Linux, whether you set aio sizes or not :-( ). I think this is a bug which needs fixing but haven't yet had time to do the work to prove this to glibc maintanence. This will be increasingly important for SMB2, as the Windows redirector now properly pipelines io (which the SMB1 redirector doesn't). Currently the only way to get real aio on Linux is to use Volker's vfs_aio_fork module, which uses processes to get true async io working. Volker is also doing a lot of work making aio work correctly on Linux (he has a git branch you can track for this). Should be working properly in 3.6.x and above (that's the plan :-). aio on Solaris, HPUX, AIX and other platforms that implement the POSIX aio_XX calls without limitations should be fine. Jeremy. -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/options/samba
From: Andy Liebman on 8 Jun 2010 09:10
Thanks, Jeremy! Andy > Currently aio on Linux is horribly broken due to a conservative > glibc, which limits asynchronous requests to one outstanding one > per file descriptor (which pretty much makes all io synchronous > on Linux, whether you set aio sizes or not :-( ). I think this > is a bug which needs fixing but haven't yet had time to do the > work to prove this to glibc maintanence. This will be increasingly > important for SMB2, as the Windows redirector now properly > pipelines io (which the SMB1 redirector doesn't). > > Currently the only way to get real aio on Linux is to use > Volker's vfs_aio_fork module, which uses processes to get > true async io working. Volker is also doing a lot of work > making aio work correctly on Linux (he has a git branch > you can track for this). Should be working properly in > 3.6.x and above (that's the plan :-). > > -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/options/samba |