Messages in this thread | | | Date | Wed, 4 Jan 2012 18:19:31 +1100 | From | Dave Chinner <> | Subject | Re: [RFC 0/3]block: An IOPS based ioscheduler |
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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?
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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