On Mon, Aug 23, 2010 at 11:00:23AM -0400, Chris Mason wrote: > On Mon, Aug 23, 2010 at 10:50:31AM -0400, Christoph Hellwig wrote: > > On Mon, Aug 23, 2010 at 10:47:55AM -0400, Chris Mason wrote: > > > The aio batching code is using igrab to get an extra reference on the > > > inode so it can safely batch. igrab will go ahead and take the global > > > inode spinlock, which can be a bottleneck on large machines doing lots > > > of AIO. > > > > > > In this case, igrab isn't required because we already have a reference > > > on the file handle. It is safe to just bump the i_count directly > > > on the inode. > > > > > > Benchmarking shows this patch brings IOP/s on tons of flash up by about > > > 2.5X. > > > > There's some places in XFS where we do the same, and it showed up as a > > bottle neck before. Instead of open coding the increment we have > > a wrapper that includes and assert that the numbers is always positive. > > > > I think we really want a proper helper for general use instead of > > completly opencoding it. Yeah igrab isn't nice. Several places are calling it without checking return code too, which means they are either buggy or should be using something else. > Nick, this is about a 1 liner to fs/aio.c replacing igrab with > atomic_inc directly on the inode reference count. > > I know your scalability tree gets rid of the global, but in this case I > think it still makes sense to avoid the locking completely when the > caller knows it is safe. Do you already have something similar hiding > in the scalability tree? Yes of course :) It has just simple refcounting increment helper that can do some of the assertions. I am hoping to be able to post the inode stuff soonish and hopefully get it into Al's tree. It will pop up on fsdevel. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
