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authorLinus Torvalds <torvalds@linux-foundation.org>2016-12-13 10:19:16 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-13 10:19:16 -0800
commit36869cb93d36269f34800b3384ba7991060a69cf (patch)
tree1ff266dcb3386bb1403494aa89647a96fd2396cd /Documentation/block/cfq-iosched.txt
parent9439b3710df688d853eb6cb4851256f2c92b1797 (diff)
parent7cd54aa8438947602cf68eda1db327822b9b8e6b (diff)
Merge branch 'for-4.10/block' of git://git.kernel.dk/linux-block
Pull block layer updates from Jens Axboe: "This is the main block pull request this series. Contrary to previous release, I've kept the core and driver changes in the same branch. We always ended up having dependencies between the two for obvious reasons, so makes more sense to keep them together. That said, I'll probably try and keep more topical branches going forward, especially for cycles that end up being as busy as this one. The major parts of this pull request is: - Improved support for O_DIRECT on block devices, with a small private implementation instead of using the pig that is fs/direct-io.c. From Christoph. - Request completion tracking in a scalable fashion. This is utilized by two components in this pull, the new hybrid polling and the writeback queue throttling code. - Improved support for polling with O_DIRECT, adding a hybrid mode that combines pure polling with an initial sleep. From me. - Support for automatic throttling of writeback queues on the block side. This uses feedback from the device completion latencies to scale the queue on the block side up or down. From me. - Support from SMR drives in the block layer and for SD. From Hannes and Shaun. - Multi-connection support for nbd. From Josef. - Cleanup of request and bio flags, so we have a clear split between which are bio (or rq) private, and which ones are shared. From Christoph. - A set of patches from Bart, that improve how we handle queue stopping and starting in blk-mq. - Support for WRITE_ZEROES from Chaitanya. - Lightnvm updates from Javier/Matias. - Supoort for FC for the nvme-over-fabrics code. From James Smart. - A bunch of fixes from a whole slew of people, too many to name here" * 'for-4.10/block' of git://git.kernel.dk/linux-block: (182 commits) blk-stat: fix a few cases of missing batch flushing blk-flush: run the queue when inserting blk-mq flush elevator: make the rqhash helpers exported blk-mq: abstract out blk_mq_dispatch_rq_list() helper blk-mq: add blk_mq_start_stopped_hw_queue() block: improve handling of the magic discard payload blk-wbt: don't throttle discard or write zeroes nbd: use dev_err_ratelimited in io path nbd: reset the setup task for NBD_CLEAR_SOCK nvme-fabrics: Add FC LLDD loopback driver to test FC-NVME nvme-fabrics: Add target support for FC transport nvme-fabrics: Add host support for FC transport nvme-fabrics: Add FC transport LLDD api definitions nvme-fabrics: Add FC transport FC-NVME definitions nvme-fabrics: Add FC transport error codes to nvme.h Add type 0x28 NVME type code to scsi fc headers nvme-fabrics: patch target code in prep for FC transport support nvme-fabrics: set sqe.command_id in core not transports parser: add u64 number parser nvme-rdma: align to generic ib_event logging helper ...
Diffstat (limited to 'Documentation/block/cfq-iosched.txt')
-rw-r--r--Documentation/block/cfq-iosched.txt32
1 files changed, 16 insertions, 16 deletions
diff --git a/Documentation/block/cfq-iosched.txt b/Documentation/block/cfq-iosched.txt
index 1e4f835a659d..895bd3813115 100644
--- a/Documentation/block/cfq-iosched.txt
+++ b/Documentation/block/cfq-iosched.txt
@@ -240,11 +240,11 @@ All cfq queues doing synchronous sequential IO go on to sync-idle tree.
On this tree we idle on each queue individually.
All synchronous non-sequential queues go on sync-noidle tree. Also any
-request which are marked with REQ_NOIDLE go on this service tree. On this
-tree we do not idle on individual queues instead idle on the whole group
-of queues or the tree. So if there are 4 queues waiting for IO to dispatch
-we will idle only once last queue has dispatched the IO and there is
-no more IO on this service tree.
+synchronous write request which is not marked with REQ_IDLE goes on this
+service tree. On this tree we do not idle on individual queues instead idle
+on the whole group of queues or the tree. So if there are 4 queues waiting
+for IO to dispatch we will idle only once last queue has dispatched the IO
+and there is no more IO on this service tree.
All async writes go on async service tree. There is no idling on async
queues.
@@ -257,17 +257,17 @@ tree idling provides isolation with buffered write queues on async tree.
FAQ
===
-Q1. Why to idle at all on queues marked with REQ_NOIDLE.
+Q1. Why to idle at all on queues not marked with REQ_IDLE.
-A1. We only do tree idle (all queues on sync-noidle tree) on queues marked
- with REQ_NOIDLE. This helps in providing isolation with all the sync-idle
+A1. We only do tree idle (all queues on sync-noidle tree) on queues not marked
+ with REQ_IDLE. This helps in providing isolation with all the sync-idle
queues. Otherwise in presence of many sequential readers, other
synchronous IO might not get fair share of disk.
For example, if there are 10 sequential readers doing IO and they get
- 100ms each. If a REQ_NOIDLE request comes in, it will be scheduled
- roughly after 1 second. If after completion of REQ_NOIDLE request we
- do not idle, and after a couple of milli seconds a another REQ_NOIDLE
+ 100ms each. If a !REQ_IDLE request comes in, it will be scheduled
+ roughly after 1 second. If after completion of !REQ_IDLE request we
+ do not idle, and after a couple of milli seconds a another !REQ_IDLE
request comes in, again it will be scheduled after 1second. Repeat it
and notice how a workload can lose its disk share and suffer due to
multiple sequential readers.
@@ -276,16 +276,16 @@ A1. We only do tree idle (all queues on sync-noidle tree) on queues marked
context of fsync, and later some journaling data is written. Journaling
data comes in only after fsync has finished its IO (atleast for ext4
that seemed to be the case). Now if one decides not to idle on fsync
- thread due to REQ_NOIDLE, then next journaling write will not get
+ thread due to !REQ_IDLE, then next journaling write will not get
scheduled for another second. A process doing small fsync, will suffer
badly in presence of multiple sequential readers.
- Hence doing tree idling on threads using REQ_NOIDLE flag on requests
+ Hence doing tree idling on threads using !REQ_IDLE flag on requests
provides isolation from multiple sequential readers and at the same
time we do not idle on individual threads.
-Q2. When to specify REQ_NOIDLE
-A2. I would think whenever one is doing synchronous write and not expecting
+Q2. When to specify REQ_IDLE
+A2. I would think whenever one is doing synchronous write and expecting
more writes to be dispatched from same context soon, should be able
- to specify REQ_NOIDLE on writes and that probably should work well for
+ to specify REQ_IDLE on writes and that probably should work well for
most of the cases.