On Tue, Jan 17, 2012 at 02:19:52PM -0500, Zheng Da wrote: > Hello, > > On Mon, Jan 16, 2012 at 6:25 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > > 0xffffffff81288b6a : xfs_aio_write_newsize_update+0x3a/0x90 [kernel] > > > > Only ever taken when doing appending writes. Are you -sure- you are > > not doing appending writes? > > > This is weird. Yes, I'm sure. I use pwrite() to write data to a 4G file, > and I check the offset of each write and they are always smaller than 4G. > I instrument the code with systemtap and it shows me that ip->i_new_size > and new_size in xfs_aio_write_newsize_update are both 0. > Since in my case there is only overwrite, ip->i_new_size will always be 0 > (the only place that updates ip->i_new_size is xfs_file_aio_write_checks). > Because of the same reason, new_size returned by xfs_file_aio_write_checks > is always 0. > Is it what you expected? No idea. I don't know what the problem you are seeing is yet, or if indeed there even is a problem as I don't really understand what you are trying to do or what results you are expecting to see... Indeed, have you run the test on something other than a RAM disk and confirmed that the problem exists on a block device that has real IO latency? If your IO takes close to zero time, then there isn't any IO level concurrency you can extract from single file direct IO; it will all just serialise on the extent tree lookups. > > > 0xffffffff812829f4 : __xfs_get_blocks+0x94/0x4a0 [kernel] > > > > And for direct IO writes, this will be the block mapping lookup so > > always hit. > > > > > > What this says to me is that you are probably doing is lots of very > > small concurrent write IOs, but I'm only guessing. Can you provide > > your test case and a description of your test hardware so we can try > > to reproduce the problem? > > > I build XFS on the top of ramdisk. So yes, there is a lot of small > concurrent writes in a second. > I create a file of 4GB in XFS (the ramdisk has 5GB of space). My test > program overwrites 4G of data to the file and each time writes a page of > data randomly to the file. It's always overwriting, and no appending. The > offset of each write is always aligned to the page size. There is no > overlapping between writes. Why are you using XFS for this? tmpfs was designed to do this sort of stuff as efficiently as possible.... > So the test case is pretty simple and I think it's easy to reproduce it. > It'll be great if you can try the test case. Can you post your test code so I know what I test is exactly what you are running? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
