These stats are useful for getting a feel for the queue depth of the cgroup,
i.e., how filled up its queues are at a given instant and over the existence of
the cgroup. This ability is useful when debugging problems in the wild as it
helps understand the application's IO pattern w/o having to read through the
userspace code (coz its tedious or just not available) or w/o the ability
to run blktrace (since you may not have root access and/or not want to disturb
performance).

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

This includes both the number of bios merged into requests belonging to this
cgroup as well as the number of requests merged together.
In the past, we've observed different merging behavior across upstream kernels,
some by design some actual bugs. This stat helps a lot in debugging such
problems when applications report decreased throughput with a new kernel
version.

This needed adding an extra elevator function to capture bios being merged as I
did not want to pollute elevator code with blkiocg knowledge and hence needed
the accounting invocation to come from CFQ.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

that include some minor fixes and addresses all comments.

Changelog: (most based on Vivek Goyal's comments)
o renamed blkiocg_reset_write to blkiocg_reset_stats
o more clarification in the documentation on io_service_time and io_wait_time
o Initialize blkg->stats_lock
o rename io_add_stat to blkio_add_stat and declare it static
o use bool for direction and sync
o derive direction and sync info from existing rq methods
o use 12 for major:minor string length
o define io_service_time better to cover the NCQ case
o add a separate reset_stats interface
o make the indexed stats a 2d array to simplify macro and function pointer code
o blkio.time now exports in jiffies as before
o Added stats description in patch description and
  Documentation/cgroup/blkio-controller.txt
o Prefix all stats functions with blkio and make them static as applicable
o replace IO_TYPE_MAX with IO_TYPE_TOTAL
o Moved #define constant to top of blk-cgroup.c
o Pass dev_t around instead of char *
o Add note to documentation file about resetting stats
o use BLK_CGROUP_MODULE in addition to BLK_CGROUP config option in #ifdef
  statements
o Avoid struct request specific knowledge in blk-cgroup. blk-cgroup.h now has
  rq_direction() and rq_sync() functions which are used by CFQ and when using
  io-controller at a higher level, bio_* functions can be added.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

We also add start_time_ns and io_start_time_ns fields to struct request
here to record the time when a request is created and when it is
dispatched to device. We use ns uints here as ms and jiffies are
not very useful for non-rotational media.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

- io_service_time
- io_wait_time
- io_serviced
- io_service_bytes

These stats are accumulated per operation type helping us to distinguish between
read and write, and sync and async IO. This patch does not increment any of
these stats.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

that info at request dispatch with other stats now. This patch removes the
existing support for accounting sectors for a blkio_group. This will be added
back differently in the next two patches.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Modify the Block I/O cgroup subsystem to be able to be built as a module.
As the CFQ disk scheduler optionally depends on blk-cgroup, config options
in block/Kconfig, block/Kconfig.iosched, and block/blk-cgroup.h are
enhanced to support the new module dependency.
Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

There's no need to take css reference here, for the caller
has already called rcu_read_lock() to prevent cgroup from
being removed.
Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
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>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

o Export disk time and sector used by a group to user space through cgroup
  interface.

o Also export a "dequeue" interface to cgroup which keeps track of how many
  a times a group was deleted from service tree. Helps in debugging.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

o Some debugging aids for CFQ.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

o One can choose to change elevator or delete a cgroup. Implement group
  reference counting so that both elevator exit and cgroup deletion can
  take place gracefully.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Nauman Rafique <nauman@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

o This is basic implementation of blkio controller cgroup interface. This is
  the common interface visible to user space and should be used by different
  IO control policies as we implement those.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>