Revert "fs: add read_iter and write_iter to several file systems"

This reverts commit 5cec9049b1c61bb08ca63928e033a0c4968aabbf.
sync: don't block the flusher thread waiting on IO

When sync does it's WB_SYNC_ALL writeback, it issues data Io and
then immediately waits for IO completion. This is done in the
context of the flusher thread, and hence completely ties up the
flusher thread for the backing device until all the dirty inodes
have been synced. On filesystems that are dirtying inodes constantly
and quickly, this means the flusher thread can be tied up for
minutes per sync call and hence badly affect system level write IO
performance as the page cache cannot be cleaned quickly.

We already have a wait loop for IO completion for sync(2), so cut
this out of the flusher thread and delegate it to wait_sb_inodes().
Hence we can do rapid IO submission, and then wait for it all to
complete.

Effect of sync on fsmark before the patch:

FSUse%        Count         Size    Files/sec     App Overhead
.....
     0       640000         4096      35154.6          1026984
     0       720000         4096      36740.3          1023844
     0       800000         4096      36184.6           916599
     0       880000         4096       1282.7          1054367
     0       960000         4096       3951.3           918773
     0      1040000         4096      40646.2           996448
     0      1120000         4096      43610.1           895647
     0      1200000         4096      40333.1           921048

And a single sync pass took:

  real    0m52.407s
  user    0m0.000s
  sys     0m0.090s

After the patch, there is no impact on fsmark results, and each
individual sync(2) operation run concurrently with the same fsmark
workload takes roughly 7s:

  real    0m6.930s
  user    0m0.000s
  sys     0m0.039s

IOWs, sync is 7-8x faster on a busy filesystem and does not have an
adverse impact on ongoing async data write operations.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
sched/rt: Remove redundant nr_cpus_allowed test

Date	Fri, 4 Oct 2013 14:24:53 -0500

From: Shawn Bohrer <sbohrer@rgmadvisors.com>

In 76854c7e8f3f4172fef091e78d88b3b751463ac6 "sched: Use
rt.nr_cpus_allowed to recover select_task_rq() cycles" an optimization
was added to select_task_rq_rt() that immediately returns when
p->nr_cpus_allowed == 1 at the beginning of the function.  This makes
the latter p->nr_cpus_allowed > 1 check redundant and can be removed.
Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>

Signed-off-by: Paul Reioux <reioux@gmail.com>
nohz: stat: Fix CPU idle time accounting

Since cpustat[CPUTIME_IDLE] is never connected to ts->idle_sleeptime,
never read from cpustat[CPUTIME_IDLE] when reporting stats in
/proc/stat.

Note this was rejected by Michal Hocko when it was initially proposed
by Martin Schwidefsky in LKML, so if you want to upstream it, better
find an alternative (either completely disable cpustat[CPUTIME_IDLE]
for CONFIG_NO_HZ or somehow connect them to keep them in sync.)

bug 1190321

Change-Id: Idc92488910b826aff850a010016d8326c7ab9e6c
Signed-off-by: Bo Yan <byan@nvidia.com>
Reviewed-on: http://git-master/r/214638
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Liang Cheng (SW) <licheng@nvidia.com>
Tested-by: Liang Cheng (SW) <licheng@nvidia.com>