On Thu, Jan 19, 2012 at 01:16:10PM -0800, Frank Mayhar wrote: > On Wed, 2012-01-18 at 20:02 +0800, Zheng Liu wrote: > > For this project, do you have a schedule? Would you like to share to me? This > > lock contention heavily impacts the performance of direct IO in our production > > environment. So we hope to improve it ASAP. > > > > I have done some direct IO benchmarks to compare ext4 with xfs using fio > > in Intel SSD. The result shows that, in direct IO, xfs outperforms ext4 and > > ext4 with dioread_nolock. > > > > To understand the effect of lock contention, I define a new function called > > ext4_file_aio_write() that calls __generic_file_aio_write() without acquiring > > i_mutex lock. Meanwhile, I remove DIO_LOCKING flag when __blockdev_direct_IO() > > is called and do the similar benchmarks. The result shows that the performance > > in ext4 is almost the same to the xfs. Thus, it proves that the i_mutex heavily > > impacts the performance. Hopefully the result is useful for you. :-) > > For the record, I have a patchset that, while not affecting i_mutex (or > locking in general), does allow AIO append writes to actually be done > asynchronously. (Currently they're forced to be done synchronously.) > It makes a big difference in performance for that particular case, even > for spinning media. Performance roughly doubled when testing with fio > against a regular two-terabyte drive; the performance improvement > against SSD would have to be much greater. > > One day soon I'll accumulate enough spare time to port the patchset > forward to the latest kernel and submit it here. Interesting. I think it might help us to improve this issue. So could you please post your test case and result in detail? Thank you. :-) Regards, Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
