writeback: fix occasional slow sync(1)
In case when system contains no dirty pages, wakeup_flusher_threads() will
submit WB_SYNC_NONE writeback for 0 pages so wb_writeback() exits
immediately without doing anything, even though there are dirty inodes in
the system.  Thus sync(1) will write all the dirty inodes from a
WB_SYNC_ALL writeback pass which is slow.

Fix the problem by using get_nr_dirty_pages() in wakeup_flusher_threads()
instead of calculating number of dirty pages manually.  That function also
takes number of dirty inodes into account.

Change-Id: Ic90f80a31bb866b7628143b8b013871f83d05c13
Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Paul Taysom <taysom@chromium.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cpufreq: Add cpu-boost driver

When certain bursty and important events take place, it might take a while
for the current cpufreq governor to notice the new load and react to it.
That would result in poor user experience. To alleviate this, the cpu-boost
driver boosts the frequency of a CPU for a short duration to maintain good
user experience while the governor catches up.

Specifically, this commit deals with ensuring that when "important" tasks
migrate from a fast CPU to a slow CPU, the frequency of the slow CPU is
boosted to be at least as high as the fast CPU for a short duration.

Since this driver enforces the boost by hooking into standard cpufreq
ADJUST notifiers, it has several advantages:
- More portable across kernel versions where the cpufreq internals might
  have been rewritten.
- Governor agnostic and hence works with multiple governors like
  conservative, ondemand, interactive, etc.
- Does not affect the sampling period/logic of existing governors.
- Can have the boost period adjusted independent of governor sampling
  period.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>

Change-Id: Ibd814a20043d0aba64ee7637a4a79b9ffa1b0991
cpufreq: Add a sync limit to cpu-boost

Perform frequency synchronization only when source CPU's frequency
is less than sync_threshold, else sync to the sync_threshold.

Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>

Change-Id: I544c414568d4e015b80ce5891dd215275bac95da
cpu boost: backport missing functions from 3.4 (DerTeufel)
reference: http://webcache.googleusercontent.com/search?q=cache:7y4Vnjzxo6wJ:androidfilesgit.org/MaC/android_kernel_jewel/commit/8e9f9bdc0bb75222891cb39389fef6910dcb085d.diff+&cd=1&hl=en&ct=clnk&gl=il

thx to dorimanx for commiting cpu boost to his 3.12 kernel. i would have missed this driver without him

Change-Id: I3cd786129f7eff14bb775194919c803566e07f25 (reverted from commit 1be7bb8d895ae518fd9459614ec7848802278ddd)
sync: Google Sync Driver for previous commit