Messages in this thread | | | From | Tejun Heo <> | Subject | [PATCH Linux 2.6.12-rc6-mm1 00/06] blk: generic dispatch queue (for review) | Date | Thu, 16 Jun 2005 13:56:38 +0900 (KST) |
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Hello, Jens.
This patchset implements generic dispatch queue I've talked about in the last ordered reimplementation patchset. The patches are against 2.6.12-rc6-mm1 + ordered patchset + 3 last blk fix patches. As I haven't posted ordered patchset against 2.6.12-rc6-mm1 (still waiting for your comments), to apply this patchset, you'll have to apply the ordered patchset against 2.6.12-rc5-mm2 to 2.6.12-rc6-mm1, and then apply these patches. libata changes will fail but it wouldn't matter for review purpose. (if you want ordered patchset against 2.6.12-rc6-mm1, I can send it to you, just tell me.)
This patchset updates only noop and cfq io schedulers. as and deadline wouldn't compile w/ this patchset applied. I'll update as and deadline once some consensus regarding the general direction of this patchset is gained.
This patchset is composed of two large parts.
* Implementation of generic dispatch queue & updating individual elevators. * Move last_merge handling into generic elevator.
Currently, each specific iosched maintains its own dispatch queue to handle ordering, requeueing, cluster dispatching, etc... This causes the following problems.
* duplicated codes * difficult to enforce semantics over dispatch queue (request ordering, requeueing, ...) * specific ioscheds have to deal with non-fs or ordered requests directly.
With generic dispatch queue, specific ioscheds are guaranteed to be handed only non-barrier fs requests, such that ioscheds only have to implement ordering logic of normal fs requests. Also, callback invocation is stricter now. Each fs request follows one of the following paths.
* add_req_fn -> dispatch_fn -> activate_fn (-> deactivate_fn -> activate_fn)* -> completed_req_fn * add_req_fn -> merged_req_fn * add_req_fn -> dispatch_fn (This path is special case for barrier request. This can be easily removed by activating at the start of ordered sequence, and completing at the end. Would removing this path be better?)
Previously, elv_remove_request() and elv_completed_request() weren't invoked for requests which are allocated outside blk layer (!rq->rl); however, other elevator/iosched functions are called for such requests making things a bit confusing. As this patchset prevents non-fs requests from going into specific ioscheds and removing the inconsistency is necessary for implementation. rq->rl tests in those places are removed.
With generic dispatch queue implemented, last_merge handling can be moved into generic elevator proper. The latter part of this patchset does that. One problem this change introduces is that, noop iosched loses its ability to merge requests (as no merging is allowed for requests on a generic dispatch queue). To add it back cleanly, we need to make noop use a separate list instead of q->queue_head to keep requests before dispatching. I don't know how meaningful this would be. The change should be simple & easy. If merging capability of noop iosched is important, plz let me know.
As this patchset makes enforcing semantics over dispatch queue easier, we can implement proper requeueing of failed tagged ordered requests (the ordered request and in-flight normal requests should be requeued in proper positions) on this. After this patchset is applied, I'll work on that.
Oh, hacks introduced in the ordered patchset (blk_account_rq modification and bar_rq_hack_*) are removed by this patchset.
[ Start of patch descriptions ]
01_blk_dispatch_queue.patch : implement generic dispatch queue
Implements generic dispatch queue which can replace all dispatch queues implemented by each iosched. This reduces code duplication, eases enforcing semantics over dispatch queue, and simplifies specific ioscheds.
02_blk_dispatch_queue_noop.patch : update noop iosched to use generic dispatch queue
Update noop iosched to use generic dispatch queue
03_blk_dispatch_queue_cfq.patch : update cfq iosched to use generic dispatch queue
Update cfq iosched to use generic dispatch queue
04_blk_last_merge_consolidation.patch : move last_merge handling into generic elevator code
Currently, both generic elevator code and specific ioscheds participate in the management and usage of last_merge. This and the following patches move last_merge handling into generic elevator code.
05_blk_last_merge_consolidation_noop.patch : remove last_merge handling from noop iosched
Remove last_merge handling from noop iosched. This change removes merging capability of noop iosched.
06_blk_last_merge_consolidation_cfq.patch : remove last_merge handling from cfq iosched
Remove last_merge handling from cfq iosched
[ End of patch descriptions ]
Thanks.
-- tejun
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