On Mon, Mar 14, 2016 at 09:54:06AM +0000, Thanos Makatos wrote: > (I've already reported this issue to centos and centos-devel. and > waited long enough but didn't get any reply.) > > I'm evaluating dm-cache on CentOS 6 kernels 3.18.21-17.el6.x86_64 (Xen 4) and > 2.6.32-573.7.1.el6.x86_64 (KVM). The test I do is a simple sequential > read using dd(1). read_promote_adjustment and sequential_threshold > have been set to 1 and 0, respectively. For the 2.6.32 kernel, all > seems to be working fine, "#usedcacheblocks" correctly reflects the > number of cached blocks based on what I'm reading with dd(1), > performance is pretty much native SSD performance. However, the same > test on the 3.18.21-17.el6.x86_64 kernel results in "#usedcacheblocks" > being stuck to "2" and no performance improvement is observed. > > Any ideas what could be wrong? How can I further debug this? There may not be anything wrong, dm-cache is very cagey these days about promoting blocks to the ssd without evidence that they're hotspots. Hitting blocks once with a dd is not enough. - Joe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
