linux-toradex.git/block/cfq-iosched.c, branch v3.2.7

block, cfq: fix empty queue crash caused by request merge

2011-12-16T13:04:23+00:00

All requests of a queue could be merged to other requests of other queue.
Such queue will not have request in it, but it's in service tree. This
will cause kernel oops.
I encounter a BUG_ON() in cfq_dispatch_request() with next patch, but the
issue should exist without the patch.

Signed-off-by: Shaohua Li 
Signed-off-by: Jens Axboe

cfq-iosched: fix cfq_cic_link() race confition

2011-12-02T09:07:07+00:00

cfq_cic_link() has race condition. When some processes which shared ioc
issue I/O to same block device simultaneously, cfq_cic_link() returns -EEXIST
sometimes. The race condition might stop I/O by following steps:

step  1: Process A: Issue an I/O to /dev/sda
step  2: Process A: Get an ioc (iocA here) in get_io_context() which does not
		    linked with a cic for the device
step  3: Process A: Get a new cic for the device (cicA here) in
		    cfq_alloc_io_context()

step  4: Process B: Issue an I/O to /dev/sda
step  5: Process B: Get iocA in get_io_context() since process A and B share the
		    same ioc
step  6: Process B: Get a new cic for the device (cicB here) in
		    cfq_alloc_io_context() since iocA has not been linked with a
		    cic for the device yet

step  7: Process A: Link cicA to iocA in cfq_cic_link()
step  8: Process A: Dispatch I/O to driver and finish it

step  9: Process B: Try to link cicB to iocA in cfq_cic_link()
		    But it fails with showing "cfq: cic link failed!" kernel
		    message, since iocA has already linked with cicA at step 7.
step 10: Process B: Wait for finishig I/O in get_request_wait()
		    The function does not wake up, when there is no I/O to the
		    device.

When cfq_cic_link() returns -EEXIST, it means ioc has already linked with cic.
So when cfq_cic_link() return -EEXIST, retry cfq_cic_lookup().

Signed-off-by: Yasuaki Ishimatsu 
Cc: stable@kernel.org
Signed-off-by: Jens Axboe

cfq-iosched: free cic_index if blkio_alloc_blkg_stats fails

2011-11-30T14:47:48+00:00

If we fail allocating the blkpg stats, we free cfqd and cfgq.
But we need to free the IDA cfqd->cic_index as well.

Signed-off-by: majianpeng 
Cc: stable@kernel.org
Signed-off-by: Jens Axboe

block: separate priority boosting from REQ_META

2011-08-23T12:50:29+00:00

Add a new REQ_PRIO to let requests preempt others in the cfq I/O schedule,
and lave REQ_META purely for marking requests as metadata in blktrace.

All existing callers of REQ_META except for XFS are updated to also
set REQ_PRIO for now.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Namhyung Kim 
Signed-off-by: Jens Axboe

Revert "cfq: Remove special treatment for metadata rqs."

2011-08-19T06:34:48+00:00

We have a kernel build regression since 3.1-rc1, which is about 10%
regression. The kernel source is in an ext3 filesystem.
Alex Shi bisect it to commit:
commit a07405b7802691d29ab3b23bdc76ee6d006aad0b
Author: Justin TerAvest 
Date:   Sun Jul 10 22:09:19 2011 +0200

    cfq: Remove special treatment for metadata rqs.

Apparently this is caused by lack metadata preemption, where ext3/ext4
do use READ_META. I didn't see a way to fix the issue, so suggest
reverting the patch.

This reverts commit a07405b7802691d29ab3b23bdc76ee6d006aad0b.

Reported-by: Alex Shi
Reported-by: Shaohua Li
Signed-off-by: Jens Axboe

cfq-iosched: Reduce linked group count upon group destruction

2011-08-02T07:24:09+00:00

FQ keeps track of number of groups which are linked on blkcg->blkg_list.
This is useful to avoid races between queue exit and cgroup exit code
paths. So if at the request queue exit time linked group count is not
zero, that means there are some group out there which is yet to be
deleted under rcu read period and queue exit code should wait for
on rcu period.

In my previous patch I forgot to decrease the number of group count.
So in current form, we nr_blkcg_linked_grps is always non-zero and
we will always wait one rcu period (if BLK_CGROUP=y). The side effect
of this is that it can increase boot time. I am surprised, nobody
complained so far.

Signed-off-by: Vivek Goyal 
Signed-off-by: Jens Axboe

CFQ: add think time check for group

2011-07-12T12:24:56+00:00

Currently when the last queue of a group has no request, we don't expire
the queue to hope request from the group comes soon, so the group doesn't
miss its share. But if the think time is big, the assumption isn't correct
and we just waste bandwidth. In such case, we don't do idle.

[global]
runtime=30
direct=1

[test1]
cgroup=test1
cgroup_weight=1000
rw=randread
ioengine=libaio
size=500m
runtime=30
directory=/mnt
filename=file1
thinktime=9000

[test2]
cgroup=test2
cgroup_weight=1000
rw=randread
ioengine=libaio
size=500m
runtime=30
directory=/mnt
filename=file2

	patched		base
test1	64k		39k
test2	548k		540k
total	604k		578k

group1 gets much better throughput because it waits less time.

To check if the patch changes behavior of queue without think time. I also
tried to give test1 2ms think time or no think time. The test result is stable.
The thoughput doesn't change with/without the patch.

Signed-off-by: Shaohua Li 
Acked-by: Vivek Goyal 
Signed-off-by: Jens Axboe

CFQ: add think time check for service tree

2011-07-12T12:24:55+00:00

Currently when the last queue of a service tree has no request, we don't
expire the queue to hope request from the service tree comes soon, so the
service tree doesn't miss its share. But if the think time is big, the
assumption isn't correct and we just waste bandwidth. In such case, we
don't do idle.

[global]
runtime=10
direct=1

[test1]
rw=randread
ioengine=libaio
size=500m
directory=/mnt
filename=file1
thinktime=9000

[test2]
rw=read
ioengine=libaio
size=1G
directory=/mnt
filename=file2

	patched		base
test1	41k/s		33k/s
test2	15868k/s	15789k/s
total	15902k/s	15817k/s

A slightly better

To check if the patch changes behavior of queue without think time. I also
tried to give test1 2ms think time or no think time. The test has variation
even without the patch, but the average throughput doesn't change with/without
the patch.

Signed-off-by: Shaohua Li 
Acked-by: Vivek Goyal 
Signed-off-by: Jens Axboe

CFQ: move think time check variables to a separate struct

2011-07-12T12:24:35+00:00

Move the variables to do think time check to a sepatate struct. This is
to prepare adding think time check for service tree and group. No
functional change.

Signed-off-by: Shaohua Li 
Acked-by: Vivek Goyal 
Signed-off-by: Jens Axboe

fixlet: Remove fs_excl from struct task.

2011-07-12T06:35:10+00:00

fs_excl is a poor man's priority inheritance for filesystems to hint to
the block layer that an operation is important. It was never clearly
specified, not widely adopted, and will not prevent starvation in many
cases (like across cgroups).

fs_excl was introduced with the time sliced CFQ IO scheduler, to
indicate when a process held FS exclusive resources and thus needed
a boost.

It doesn't cover all file systems, and it was never fully complete.
Lets kill it.

Signed-off-by: Justin TerAvest 
Signed-off-by: Jens Axboe