[Adding dm-crypt + linux-kernel] On Mon, Mar 25, 2013 at 11:47:22PM -0400, Mikulas Patocka wrote: > I performed some dm-crypt performance tests as Mike suggested. > > It turns out that unbound workqueue performance has improved somewhere > between kernel 3.2 (when I made the dm-crypt patches) and 3.8, so the > patches for hand-built dispatch are no longer needed. > > For RAID-0 composed of two disks with total throughput 260MB/s, the > unbound workqueue performs as well as the hand-built dispatch (both > sustain the 260MB/s transfer rate). > > For ramdisk, unbound workqueue performs better than hand-built dispatch > (620MB/s vs 400MB/s). Unbound workqueue with the patch that Mike suggested > (git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git) improves > performance slighlty on ramdisk compared to 3.8 (700MB/s vs. 620MB/s). > > > > However, there is still the problem with request ordering. Milan found out > that under some circumstances parallel dm-crypt has worse performance than > the previous dm-crypt code. I found out that this is not caused by > deficiencies in the code that distributes work to individual processors. > Performance drop is caused by the fact that distributing write bios to > multiple processors causes the encryption to finish out of order and the > I/O scheduler is unable to merge these out-of-order bios. > > The deadline and noop schedulers perform better (only 50% slowdown > compared to old dm-crypt), CFQ performs very badly (8 times slowdown). > > > If I sort the requests in dm-crypt to come out in the same order as they > were received, there is no longer any slowdown, the new crypt performs as > well as the old crypt, but the last time I submitted the patches, people > objected to sorting requests in dm-crypt, saying that the I/O scheduler > should sort them. But it doesn't. This problem still persists in the > current kernels. > > > For best performance we could use the unbound workqueue implementation > with request sorting, if people don't object to the request sorting being > done in dm-crypt. On Tue, Mar 26, 2013 at 02:52:29AM -0400, Christoph Hellwig wrote: > FYI, XFS also does it's own request ordering for the metadata buffers, > because it knows the needed ordering and has a bigger view than than > than especially CFQ. You at least have precedence in a widely used > subsystem for this code. So please post this updated version of the patches for a wider group of people to try out. Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
