Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Wed, 27 Jul 2011 17:08:28 -0400 > Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > >> On Mon, Jun 20, 2011 at 04:17:35PM -0700, Dan Ehrenberg wrote: >> > The fast path does not apply for operations of the wrong size >> > or alignmnent, or for operations on raw drives with 512-byte sectors. >> > It might be possible to make this special case a little more general >> > while maintaining its performance benefits, but I do not believe that >> > the full performance benefits can be achieved without resorting to >> > special handling of simple cases, as is done in this patch. >> >> Did you check how this compares to Andis small optimizations? >> >> Also operations on raw disks are something people with fast devices >> care about a lot. We often hear about benchmark regressions due to >> stupid little things in the direct I/O code. >> >> If we want to special case something that would be a very easy target, >> with a 1:1 mapping of logical to physical blocks and thus no need >> to call the allocator first, and no need for any kind of locking >> or alignment handling. > > Ken did this back in 2006 > (http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e61c90188b9956edae1105eef361d8981a352fcd) > but we reverted that shortly afterwards for some reason. For this reason: commit b2e895dbd80c420bfc0937c3729b4afe073b3848 Author: Andrew Morton <akpm@xxxxxxxx> Date: Sat Feb 3 01:14:01 2007 -0800 [PATCH] revert blockdev direct io back to 2.6.19 version Andrew Vasquez is reporting as-iosched oopses and a 65% throughput slowdown due to the recent special-casing of direct-io against blockdevs. We don't know why either of these things are occurring. The patch minimally reverts us back to the 2.6.19 code for a 2.6.20 release. -- 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
