This patch change DM_ULOG_REQUEST_VERSION from 2 to 3. It could tell cmirrord that kernel is now supporting delay some flushes, and cmirrord will do someting accordingly. Based on my test result, the cluster raid1 writes loss 80% performance. I found that the most time is occupied by the function userspace_flush. Usually userspace_flush needs three stages(mark, clear, flush)to communicate with cmirrord. >From the cmirrord's perspective, mark and flush functions run cluster_send first and then return to the kernel. In other words, the requests of mark_region and flush in userspace_flush at least require a cluster_send period to finish. this is the root cause of bad performance. The idea is to merge flush and mark request together in both cmirrord and dm-log-userspace. We run clog_flush directly after clog_mark_region. So the userspace_flush do not have to request flush again after requesting mark_region. Moreover, I think the flush of clear region could be delayed. If we have both mark and clear region, only sending a mark_region request is OK, because clog_flush will automatically run.(ignore the clean_region time). It only takes one cluster_send period. If we have only mark region, a mark_region request is also OK, it takes one cluster_send period. If we have only clear_region, we could delay the flush of cleared_region for 3 seconds. Overall, before the patch, mark_region require approximately two cluster_send period(mark_region and flush), after the patch, mark_region only needs one cluster_send period. Based on my test, the performance is as twice as before. dongmao zhang (2): improve the performance of dm-log-userspace change API of dm-log-userspace to support delay flush drivers/md/dm-log-userspace-base.c | 109 ++++++++++++++++++++++++++++++--- include/uapi/linux/dm-log-userspace.h | 2 +- 2 files changed, 101 insertions(+), 10 deletions(-) -- 1.7.3.4 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
