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Commit a2b80967 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

block: replace REQ_NOIDLE with REQ_IDLE 



Noidle should be the default for writes as seen by all the compounds
definitions in fs.h using it.  In fact only direct I/O really should
be using NODILE, so turn the whole flag around to get the defaults
right, which will make our life much easier especially onces the
WRITE_* defines go away.

This assumes all the existing "raw" users of REQ_SYNC for writes
want noidle behavior, which seems to be spot on from a quick audit.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent b685d3d6

Documentation/block/cfq-iosched.txt

+16 −16
Original line number Diff line number Diff line
@@ -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.

block/cfq-iosched.c

+8 −3
Original line number Diff line number Diff line
@@ -3914,6 +3914,12 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
		cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);

}



static inline bool req_noidle(struct request *req)

{

	return req_op(req) == REQ_OP_WRITE &&

		(req->cmd_flags & (REQ_SYNC | REQ_IDLE)) == REQ_SYNC;

}



/*

 * Disable idle window if the process thinks too long or seeks so much that

 * it doesn't matter
@@ -3935,7 +3941,7 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
	if (cfqq->queued[0] + cfqq->queued[1] >= 4)

		cfq_mark_cfqq_deep(cfqq);



	if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))

	if (cfqq->next_rq && req_noidle(cfqq->next_rq))

		enable_idle = 0;

	else if (!atomic_read(&cic->icq.ioc->active_ref) ||

		 !cfqd->cfq_slice_idle ||
@@ -4220,8 +4226,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) 
	const int sync = rq_is_sync(rq);

	u64 now = ktime_get_ns();



	cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d",

		     !!(rq->cmd_flags & REQ_NOIDLE));

	cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d", req_noidle(rq));



	cfq_update_hw_tag(cfqd);

drivers/block/drbd/drbd_actlog.c

+1 −1
Original line number Diff line number Diff line
@@ -148,7 +148,7 @@ static int _drbd_md_sync_page_io(struct drbd_device *device, 


	if ((op == REQ_OP_WRITE) && !test_bit(MD_NO_FUA, &device->flags))

		op_flags |= REQ_FUA | REQ_PREFLUSH;

	op_flags |= REQ_SYNC | REQ_NOIDLE;

	op_flags |= REQ_SYNC;



	bio = bio_alloc_drbd(GFP_NOIO);

	bio->bi_bdev = bdev->md_bdev;

include/linux/blk_types.h

+2 −2
Original line number Diff line number Diff line
@@ -175,7 +175,7 @@ enum req_flag_bits { 
	__REQ_META,		/* metadata io request */

	__REQ_PRIO,		/* boost priority in cfq */

	__REQ_NOMERGE,		/* don't touch this for merging */

	__REQ_NOIDLE,		/* don't anticipate more IO after this one */

	__REQ_IDLE,		/* anticipate more IO after this one */

	__REQ_INTEGRITY,	/* I/O includes block integrity payload */

	__REQ_FUA,		/* forced unit access */

	__REQ_PREFLUSH,		/* request for cache flush */
@@ -190,7 +190,7 @@ enum req_flag_bits { 
#define REQ_META		(1ULL << __REQ_META)

#define REQ_PRIO		(1ULL << __REQ_PRIO)

#define REQ_NOMERGE		(1ULL << __REQ_NOMERGE)

#define REQ_NOIDLE		(1ULL << __REQ_NOIDLE)

#define REQ_IDLE		(1ULL << __REQ_IDLE)

#define REQ_INTEGRITY		(1ULL << __REQ_INTEGRITY)

#define REQ_FUA			(1ULL << __REQ_FUA)

#define REQ_PREFLUSH		(1ULL << __REQ_PREFLUSH)

include/linux/fs.h

+5 −5
Original line number Diff line number Diff line
@@ -197,11 +197,11 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, 
#define WRITE			REQ_OP_WRITE



#define READ_SYNC		0

#define WRITE_SYNC		(REQ_SYNC | REQ_NOIDLE)

#define WRITE_ODIRECT		REQ_SYNC

#define WRITE_FLUSH		(REQ_NOIDLE | REQ_PREFLUSH)

#define WRITE_FUA		(REQ_NOIDLE | REQ_FUA)

#define WRITE_FLUSH_FUA		(REQ_NOIDLE | REQ_PREFLUSH | REQ_FUA)

#define WRITE_SYNC		REQ_SYNC

#define WRITE_ODIRECT		(REQ_SYNC | REQ_IDLE)

#define WRITE_FLUSH		REQ_PREFLUSH

#define WRITE_FUA		REQ_FUA

#define WRITE_FLUSH_FUA		(REQ_PREFLUSH | REQ_FUA)



/*

 * Attribute flags.  These should be or-ed together to figure out what