On Tue, Oct 12, 2010 at 04:14:55PM +0200, Christoph Hellwig wrote: > I still think adding code to every filesystem to optimize for a rather > stupid use case is not a good idea. I dropped out a bit from the > thread in the middle, but what was the real use case for lots of > concurrent fsyncs on the same inode again? The use case I'm looking at is concurrent fsyncs on /different/ inodes, actually. We have _n_ different processes, each writing (and fsyncing) its own separate file on the same filesystem. iirc, ext4_sync_file is called with the inode mutex held, which prevents concurrent fsyncs on the same inode. > And what is the amount of performance you need? If we go back to the > direct submission of REQ_FLUSH request from the earlier flush+fua > setups that were faster or high end storage, would that be enough for > you? > > Below is a patch brining the optimization back. > > WARNING: completely untested! So I hacked up a patch to the block layer that collects measurements of the time delay between blk_start_request and blk_finish_request when a flush command is encountered, and what I noticed was that there's a rather large discrepancy between the delay as observed by the block layer and the delay as observed by ext4. In general, the discrepancy is a nearly 2x increase between what the block layer sees and what ext4 sees, so I'll give Christoph's direct-flush patch (below) a try over the weekend. --D -- 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
