Currently we split seeky coop queues after 1s, which is too big. Below patch
marks seeky coop queue split_coop flag after one slice. After that, if new
requests come in, the queues will be splitted. Patch is suggested by Corrado.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Reviewed-by: Corrado Zoccolo <czoccolo@gmail.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Few weeks back, Shaohua Li had posted similar patch. I am reposting it
with more test results.
This patch does two things.
- Do not idle on async queues.
- It also changes the write queue depth CFQ drives (cfq_may_dispatch()).
Currently, we seem to driving queue depth of 1 always for WRITES. This is
true even if there is only one write queue in the system and all the logic
of infinite queue depth in case of single busy queue as well as slowly
increasing queue depth based on last delayed sync request does not seem to
be kicking in at all.
This patch will allow deeper WRITE queue depths (subjected to the other
WRITE queue depth contstraints like cfq_quantum and last delayed sync
request).
Shaohua Li had reported getting more out of his SSD. For me, I have got
one Lun exported from an HP EVA and when pure buffered writes are on, I
can get more out of the system. Following are test results of pure
buffered writes (with end_fsync=1) with vanilla and patched kernel. These
results are average of 3 sets of run with increasing number of threads.
AVERAGE[bufwfs][vanilla]
-------
job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us)
--- --- -- ------------ ----------- ------------- -----------
bufwfs 3 1 0 0 95349 474141
bufwfs 3 2 0 0 100282 806926
bufwfs 3 4 0 0 109989 2.7301e+06
bufwfs 3 8 0 0 116642 3762231
bufwfs 3 16 0 0 118230 6902970
AVERAGE[bufwfs] [patched kernel]
-------
bufwfs 3 1 0 0 270722 404352
bufwfs 3 2 0 0 206770 1.06552e+06
bufwfs 3 4 0 0 195277 1.62283e+06
bufwfs 3 8 0 0 260960 2.62979e+06
bufwfs 3 16 0 0 299260 1.70731e+06
I also ran buffered writes along with some sequential reads and some
buffered reads going on in the system on a SATA disk because the potential
risk could be that we should not be driving queue depth higher in presence
of sync IO going to keep the max clat low.
With some random and sequential reads going on in the system on one SATA
disk I did not see any significant increase in max clat. So it looks like
other WRITE queue depth control logic is doing its job. Here are the
results.
AVERAGE[brr, bsr, bufw together] [vanilla]
-------
job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us)
--- --- -- ------------ ----------- ------------- -----------
brr 3 1 850 546345 0 0
bsr 3 1 14650 729543 0 0
bufw 3 1 0 0 23908 8274517
brr 3 2 981.333 579395 0 0
bsr 3 2 14149.7 1175689 0 0
bufw 3 2 0 0 21921 1.28108e+07
brr 3 4 898.333 1.75527e+06 0 0
bsr 3 4 12230.7 1.40072e+06 0 0
bufw 3 4 0 0 19722.3 2.4901e+07
brr 3 8 900 3160594 0 0
bsr 3 8 9282.33 1.91314e+06 0 0
bufw 3 8 0 0 18789.3 23890622
AVERAGE[brr, bsr, bufw mixed] [patched kernel]
-------
job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us)
--- --- -- ------------ ----------- ------------- -----------
brr 3 1 837 417973 0 0
bsr 3 1 14357.7 591275 0 0
bufw 3 1 0 0 24869.7 8910662
brr 3 2 1038.33 543434 0 0
bsr 3 2 13351.3 1205858 0 0
bufw 3 2 0 0 18626.3 13280370
brr 3 4 913 1.86861e+06 0 0
bsr 3 4 12652.3 1430974 0 0
bufw 3 4 0 0 15343.3 2.81305e+07
brr 3 8 890 2.92695e+06 0 0
bsr 3 8 9635.33 1.90244e+06 0 0
bufw 3 8 0 0 17200.3 24424392
So looks like it might make sense to include this patch.
Thanks
Vivek
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
In cfq_should_preempt(), we currently allow some cases where a non-RT request
can preempt an ongoing RT cfqq timeslice. This should not happen.
Examples include:
o A sync_noidle wl type non-RT request pre-empting a sync_noidle wl type cfqq
on which we are idling.
o Once we have per-cgroup async queues, a non-RT sync request pre-empting a RT
async cfqq.
Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
seek_mean could be very big sometimes, using it as close criteria is meaningless
as this doen't improve any performance. So if it's big, let's fallback to
default value.
Reviewed-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o CFQ now internally divides cfq queues in therr workload categories. sync-idle,
sync-noidle and async. Which workload to run depends primarily on rb_key
offset across three service trees. Which is a combination of mulitiple things
including what time queue got queued on the service tree.
There is one exception though. That is if we switched the prio class, say
we served some RT tasks and again started serving BE class, then with-in
BE class we always started with sync-noidle workload irrespective of rb_key
offset in service trees.
This can provide better latencies for sync-noidle workload in the presence
of RT tasks.
o This patch gets rid of that exception and which workload to run with-in
class always depends on lowest rb_key across service trees. The reason
being that now we have multiple BE class groups and if we always switch
to sync-noidle workload with-in group, we can potentially starve a sync-idle
workload with-in group. Same is true for async workload which will be in
root group. Also the workload-switching with-in group will become very
unpredictable as it now depends whether some RT workload was running in
the system or not.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Acked-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o allow_merge() already checks if submitting task is pointing to same cfqq
as rq has been queued in. If everything is fine, we should not be having
a task in one cgroup and having a pointer to cfqq in other cgroup.
Well I guess in some situations it can happen and that is, when a random
IO queue has been moved into root cgroup for group_isolation=0. In
this case, tasks's cgroup/group is different from where actually cfqq is,
but this is intentional and in this case merging should be allowed.
The second situation is where due to close cooperator patches, multiple
processes can be sharing a cfqq. If everything implemented right, we should
not end up in a situation where tasks from different processes in different
groups are sharing the same cfqq as we allow merging of cooperating queues
only if they are in same group.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
When a group is resumed, if it doesn't have workload slice left,
we should set workload_expires as expired. Otherwise, we might
start from where we left in previous group by error.
Thanks the idea from Corrado.
Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
I think my previous patch introduced a bug which can lead to CFQ hitting
BUG_ON().
The offending commit in for-2.6.33 branch is.
commit 7667aa0630
Author: Vivek Goyal <vgoyal@redhat.com>
Date: Tue Dec 8 17:52:58 2009 -0500
cfq-iosched: Take care of corner cases of group losing share due to deletion
While doing some stress testing on my box, I enountered following.
login: [ 3165.148841] BUG: scheduling while
atomic: swapper/0/0x10000100
[ 3165.149821] Modules linked in: cfq_iosched dm_multipath qla2xxx igb
scsi_transport_fc dm_snapshot [last unloaded: scsi_wait_scan]
[ 3165.149821] Pid: 0, comm: swapper Not tainted
2.6.32-block-for-33-merged-new #3
[ 3165.149821] Call Trace:
[ 3165.149821] <IRQ> [<ffffffff8103fab8>] __schedule_bug+0x5c/0x60
[ 3165.149821] [<ffffffff8103afd7>] ? __wake_up+0x44/0x4d
[ 3165.149821] [<ffffffff8153a979>] schedule+0xe3/0x7bc
[ 3165.149821] [<ffffffff8103a796>] ? cpumask_next+0x1d/0x1f
[ 3165.149821] [<ffffffffa000b21d>] ? cfq_dispatch_requests+0x6ba/0x93e
[cfq_iosched]
[ 3165.149821] [<ffffffff810422d8>] __cond_resched+0x2a/0x35
[ 3165.149821] [<ffffffffa000b21d>] ? cfq_dispatch_requests+0x6ba/0x93e
[cfq_iosched]
[ 3165.149821] [<ffffffff8153b1ee>] _cond_resched+0x2c/0x37
[ 3165.149821] [<ffffffff8100e2db>] is_valid_bugaddr+0x16/0x2f
[ 3165.149821] [<ffffffff811e4161>] report_bug+0x18/0xac
[ 3165.149821] [<ffffffff8100f1fc>] die+0x39/0x63
[ 3165.149821] [<ffffffff8153cde1>] do_trap+0x11a/0x129
[ 3165.149821] [<ffffffff8100d470>] do_invalid_op+0x96/0x9f
[ 3165.149821] [<ffffffffa000b21d>] ? cfq_dispatch_requests+0x6ba/0x93e
[cfq_iosched]
[ 3165.149821] [<ffffffff81034b4d>] ? enqueue_task+0x5c/0x67
[ 3165.149821] [<ffffffff8103ae83>] ? task_rq_unlock+0x11/0x13
[ 3165.149821] [<ffffffff81041aae>] ? try_to_wake_up+0x292/0x2a4
[ 3165.149821] [<ffffffff8100c935>] invalid_op+0x15/0x20
[ 3165.149821] [<ffffffffa000b21d>] ? cfq_dispatch_requests+0x6ba/0x93e
[cfq_iosched]
[ 3165.149821] [<ffffffff810df5a6>] ? virt_to_head_page+0xe/0x2f
[ 3165.149821] [<ffffffff811d8c2a>] blk_peek_request+0x191/0x1a7
[ 3165.149821] [<ffffffff811e5b8d>] ? kobject_get+0x1a/0x21
[ 3165.149821] [<ffffffff812c8d4c>] scsi_request_fn+0x82/0x3df
[ 3165.149821] [<ffffffff8110b2de>] ? bio_fs_destructor+0x15/0x17
[ 3165.149821] [<ffffffff810df5a6>] ? virt_to_head_page+0xe/0x2f
[ 3165.149821] [<ffffffff811d931f>] __blk_run_queue+0x42/0x71
[ 3165.149821] [<ffffffff811d9403>] blk_run_queue+0x26/0x3a
[ 3165.149821] [<ffffffff812c8761>] scsi_run_queue+0x2de/0x375
[ 3165.149821] [<ffffffff812b60ac>] ? put_device+0x17/0x19
[ 3165.149821] [<ffffffff812c92d7>] scsi_next_command+0x3b/0x4b
[ 3165.149821] [<ffffffff812c9b9f>] scsi_io_completion+0x1c9/0x3f5
[ 3165.149821] [<ffffffff812c3c36>] scsi_finish_command+0xb5/0xbe
I think I have hit following BUG_ON() in cfq_dispatch_request().
BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
Please find attached the patch to fix it. I have done some stress testing
with it and have not seen it happening again.
o We should wait on a queue even after slice expiry only if it is empty. If
queue is not empty then continue to expire it.
o If we decide to keep the queue then make cfqq=NULL. Otherwise select_queue()
will return a valid cfqq and cfq_dispatch_request() can hit following
BUG_ON().
BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list))
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Remove wait_request flag when idle time is being deleted, otherwise
it'll hit this path every time when a request is enqueued.
Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
If there is a sequential reader running in a group, we wait for next request
to come in that group after slice expiry and once new request is in, we expire
the queue. Otherwise we delete the group from service tree and group looses
its fair share.
So far I was marking a queue as wait_busy if it had consumed its slice and
it was last queue in the group. But this condition did not cover following
two cases.
1.If a request completed and slice has not expired yet. Next request comes
in and is dispatched to disk. Now select_queue() hits and slice has expired.
This group will be deleted. Because request is still in the disk, this queue
will never get a chance to wait_busy.
2.If request completed and slice has not expired yet. Before next request
comes in (delay due to think time), select_queue() hits and expires the
queue hence group. This queue never got a chance to wait busy.
Gui was hitting the boundary condition 1 and not getting fairness numbers
proportional to weight.
This patch puts the checks for above two conditions and improves the fairness
numbers for sequential workload on rotational media. Check in select_queue()
takes care of case 1 and additional check in should_wait_busy() takes care
of case 2.
Reported-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o Get rid of wait_busy_done flag. This flag only tells we were doing wait
busy on a queue and that queue got request so expire it. That information
can easily be obtained by (cfq_cfqq_wait_busy() && queue_is_not_empty). So
remove this flag and keep code simple.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
It doesn't make any sense to try to find out a close cooperating
queue if current cfqq is the only one in the group.
Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
The introduction of ramp-up formula for async queue depths has
slowed down dirty page reclaim, by reducing async write performance.
This patch makes sure the formula kicks in only when sync request
was recently delayed.
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Fix a crash during boot reported by Jeff Moyer. Fix the issue of accessing
cfqq after freeing it.
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@carl.(none)>
After the merge of the IO controller patches, booting on my megaraid
box ran much slower. Vivek Goyal traced it down to megaraid discovery
creating tons of devices, each suffering a grace period when they later
kill that queue (if no device is found).
So lets use call_rcu() to batch these deferred frees, instead of taking
the grace period hit for each one.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o One of the goals of block IO controller is that it should be able to
support mulitple io control policies, some of which be operational at
higher level in storage hierarchy.
o To begin with, we had one io controlling policy implemented by CFQ, and
I hard coded the CFQ functions called by blkio. This created issues when
CFQ is compiled as module.
o This patch implements a basic dynamic io controlling policy registration
functionality in blkio. This is similar to elevator functionality where
ioschedulers register the functions dynamically.
o Now in future, when more IO controlling policies are implemented, these
can dynakically register with block IO controller.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o blkio controller is inside the kernel and cfq makes use of interfaces
exported by blkio. CFQ can be a module too, hence export symbols used
by CFQ.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
cfq_arm_slice_timer() has logic to disable idle window for SSD device. The same
thing should be done at cfq_select_queue() too, otherwise we will still see
idle window. This makes the nonrot check logic consistent in cfq.
Tests in a intel SSD with low_latency knob close, below patch can triple disk
thoughput for muti-thread sequential read.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o rq_noidle() is supposed to tell cfq that do not expect a request after this
one, hence don't idle. But this does not seem to work very well. For example
for direct random readers, rq_noidle = 1 but there is next request coming
after this. Not idling, leads to a group not getting its share even if
group_isolation=1.
o The right solution for this issue is to scan the higher layers and set
right flag (WRITE_SYNC or WRITE_ODIRECT). For the time being, this single
line fix helps. This should not have any significant impact when we are
not using cgroups. I will later figure out IO paths in higher layer and
fix it.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o If a group is running only a random reader, then it will not have enough
traffic to keep disk busy and we will reduce overall throughput. This
should result in better latencies for random reader though. If we don't
idle on random reader service tree, then this random reader will experience
large latencies if there are other groups present in system with sequential
readers running in these.
o One solution suggested by corrado is that by default keep the random readers
or sync-noidle workload in root group so that during one dispatch round
we idle only once on sync-noidle tree. This means that all the sync-idle
workload queues will be in their respective group and we will see service
differentiation in those but not on sync-noidle workload.
o Provide a tunable group_isolation. If set, this will make sure that even
sync-noidle queues go in their respective group and we wait on these. This
provides stronger isolation between groups but at the expense of throughput
if group does not have enough traffic to keep the disk busy.
o By default group_isolation = 0
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o Async queues are not per group. Instead these are system wide and maintained
in root group. Hence their workload slice length should be calculated
based on total number of queues in the system and not just queues in the
root group.
o As root group's default weight is 1000, make sure to charge async queue
more in terms of vtime so that it does not get more time on disk because
root group has higher weight.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
o If a queue consumes its slice and then gets deleted from service tree, its
associated group will also get deleted from service tree if this was the
only queue in the group. That will make group loose its share.
o For the queues on which we have idling on and if these have used their
slice, wait a bit for these queues to get backlogged again and then
expire these queues so that group does not loose its share.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Shaohua Li
Vivek Goyal
Divyesh Shah
Gui Jianfeng
Corrado Zoccolo
Jens Axboe