After update_curr_dl() the current task might not be the leftmost task
anymore. In that case do not start a new hrtick for it.

In this case NEED_RESCHED will be set and the next schedule will start
the hrtick for the new task if and when appropriate.
Signed-off-by: NWanpeng Li <wanpeng.li@linux.intel.com>
Acked-by: NJuri Lelli <juri.lelli@arm.com>
[ Rewrote the changelog and comment. ]
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1416962647-76792-2-git-send-email-wanpeng.li@linux.intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>