Messages in this thread | | | Subject | Re: [RFC 0/3]block: An IOPS based ioscheduler | From | Shaohua Li <> | Date | Mon, 09 Jan 2012 09:09:35 +0800 |
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On Mon, 2012-01-09 at 09:16 +1100, Dave Chinner wrote: > On Fri, Jan 06, 2012 at 01:12:29PM +0800, Shaohua Li wrote: > > On Thu, 2012-01-05 at 14:50 +0800, Shaohua Li wrote: > > > On Wed, 2012-01-04 at 18:19 +1100, Dave Chinner wrote: > > > > On Wed, Jan 04, 2012 at 02:53:37PM +0800, Shaohua Li wrote: > > > > > An IOPS based I/O scheduler > > > > > > > > > > Flash based storage has some different characteristics against rotate disk. > > > > > 1. no I/O seek. > > > > > 2. read and write I/O cost usually is much different. > > > > > 3. Time which a request takes depends on request size. > > > > > 4. High throughput and IOPS, low latency. > > > > > > > > > > CFQ iosched does well for rotate disk, for example fair dispatching, idle > > > > > for sequential read. It also has optimization for flash based storage (for > > > > > item 1 above), but overall it's not designed for flash based storage. It's > > > > > a slice based algorithm. Since flash based storage request cost is very > > > > > low, and drive has big queue_depth is quite popular now which makes > > > > > dispatching cost even lower, CFQ's slice accounting (jiffy based) > > > > > doesn't work well. CFQ doesn't consider above item 2 & 3. > > > > > > > > > > FIOPS (Fair IOPS) ioscheduler is trying to fix the gaps. It's IOPS based, so > > > > > only targets for drive without I/O seek. It's quite similar like CFQ, but > > > > > the dispatch decision is made according to IOPS instead of slice. > > > > > > > > > > The algorithm is simple. Drive has a service tree, and each task lives in > > > > > the tree. The key into the tree is called vios (virtual I/O). Every request > > > > > has vios, which is calculated according to its ioprio, request size and so > > > > > on. Task's vios is the sum of vios of all requests it dispatches. FIOPS > > > > > always selects task with minimum vios in the service tree and let the task > > > > > dispatch request. The dispatched request's vios is then added to the task's > > > > > vios and the task is repositioned in the sevice tree. > > > > > > > > > > The series are orgnized as: > > > > > Patch 1: separate CFQ's io context management code. FIOPS will use it too. > > > > > Patch 2: The core FIOPS. > > > > > Patch 3: request read/write vios scale. This demontrates how the vios scale. > > > > > > > > > > To make the code simple for easy view, some scale code isn't included here, > > > > > some not implementated yet. > > > > > > > > > > TODO: > > > > > 1. ioprio support (have patch already) > > > > > 2. request size vios scale > > > > > 3. cgroup support > > > > > 4. tracing support > > > > > 5. automatically select default iosched according to QUEUE_FLAG_NONROT. > > > > > > > > > > Comments and suggestions are welcome! > > > > > > > > Benchmark results? > > > I didn't have data yet. The patches are still in earlier stage, I want > > > to focus on the basic idea first. > > since you asked, I tested in a 4 socket machine with 12 X25M SSD jbod, > > fs is ext4. > > > > workload percentage change with fiops against cfq > > fio_sync_read_4k -2 > > fio_mediaplay_64k 0 > > fio_mediaplay_128k 0 > > fio_mediaplay_rr_64k 0 > > fio_sync_read_rr_4k 0 > > fio_sync_write_128k 0 > > fio_sync_write_64k -1 > > fio_sync_write_4k -2 > > fio_sync_write_64k_create 0 > > fio_sync_write_rr_64k_create 0 > > fio_sync_write_128k_create 0 > > fio_aio_randread_4k -4 > > fio_aio_randread_64k 0 > > fio_aio_randwrite_4k 1 > > fio_aio_randwrite_64k 0 > > fio_aio_randrw_4k -1 > > fio_aio_randrw_64k 0 > > fio_tpch 9 > > fio_tpcc 0 > > fio_mmap_randread_4k -1 > > fio_mmap_randread_64k 1 > > fio_mmap_randread_1k -8 > > fio_mmap_randwrite_4k 35 > > fio_mmap_randwrite_64k 22 > > fio_mmap_randwrite_1k 28 > > fio_mmap_randwrite_4k_halfbusy 24 > > fio_mmap_randrw_4k 23 > > fio_mmap_randrw_64k 4 > > fio_mmap_randrw_1k 22 > > fio_mmap_randrw_4k_halfbusy 35 > > fio_mmap_sync_read_4k 0 > > fio_mmap_sync_read_64k -1 > > fio_mmap_sync_read_128k -1 > > fio_mmap_sync_read_rr_64k 5 > > fio_mmap_sync_read_rr_4k 3 > > > > The fio_mmap_randread_1k has regression against 3.2-rc7, but no > > regression against 3.2-rc6 kernel, still checking why. The fiops has > > improvement for read/write mixed workload. CFQ is known not good for > > read/write mixed workload. > > Numbers like this are meaningless without knowing what the hardware > capability is and how the numbers compare to that raw capability. > They tell me only mmap based random write improves in > performance, and only one specific type of random write improves, > not all types. > > That raises more questions that it answers: why do AIO based random > writes not go any faster? Is that because even with CFQ, AIO based > random writes saturate the device? i.e. is AIO based IO that much > faster than mmap based IO that there is no scope for improvement on > your hardware? > > You need to present raw numbers and give us some idea of how close > those numbers are to raw hardware capability for us to have any idea > what improvements these numbers actually demonstrate. Yes, your guess is right. The hardware has limitation. 12 SSD exceeds the jbod capability, for both throughput and IOPS, that's why only read/write mixed workload impacts. I'll use less SSD in later tests, which will demonstrate the performance better. I'll report both raw numbers and fiops/cfq numbers later.
Thanks, Shaohua
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