1. 24 5月, 2017 1 次提交
  2. 17 4月, 2017 1 次提交
  3. 15 4月, 2017 5 次提交
  4. 14 3月, 2017 1 次提交
  5. 02 3月, 2017 2 次提交
  6. 01 2月, 2017 4 次提交
  7. 25 12月, 2016 1 次提交
  8. 16 11月, 2016 1 次提交
  9. 15 11月, 2016 1 次提交
  10. 11 7月, 2016 1 次提交
  11. 02 3月, 2016 1 次提交
    • F
      posix-cpu-timers: Migrate to use new tick dependency mask model · b7878300
      Frederic Weisbecker 提交于
      Instead of providing asynchronous checks for the nohz subsystem to verify
      posix cpu timers tick dependency, migrate the latter to the new mask.
      
      In order to keep track of the running timers and expose the tick
      dependency accordingly, we must probe the timers queuing and dequeuing
      on threads and process lists.
      
      Unfortunately it implies both task and signal level dependencies. We
      should be able to further optimize this and merge all that on the task
      level dependency, at the cost of a bit of complexity and may be overhead.
      Reviewed-by: NChris Metcalf <cmetcalf@ezchip.com>
      Cc: Christoph Lameter <cl@linux.com>
      Cc: Chris Metcalf <cmetcalf@ezchip.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Luiz Capitulino <lcapitulino@redhat.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Viresh Kumar <viresh.kumar@linaro.org>
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      b7878300
  12. 15 10月, 2015 4 次提交
  13. 08 5月, 2015 3 次提交
    • J
      sched, timer: Use the atomic task_cputime in thread_group_cputimer · 71107445
      Jason Low 提交于
      Recent optimizations were made to thread_group_cputimer to improve its
      scalability by keeping track of cputime stats without a lock. However,
      the values were open coded to the structure, causing them to be at
      a different abstraction level from the regular task_cputime structure.
      Furthermore, any subsequent similar optimizations would not be able to
      share the new code, since they are specific to thread_group_cputimer.
      
      This patch adds the new task_cputime_atomic data structure (introduced in
      the previous patch in the series) to thread_group_cputimer for keeping
      track of the cputime atomically, which also helps generalize the code.
      Suggested-by: NIngo Molnar <mingo@kernel.org>
      Signed-off-by: NJason Low <jason.low2@hp.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Acked-by: NThomas Gleixner <tglx@linutronix.de>
      Acked-by: NRik van Riel <riel@redhat.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Aswin Chandramouleeswaran <aswin@hp.com>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Davidlohr Bueso <dave@stgolabs.net>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
      Cc: Scott J Norton <scott.norton@hp.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Waiman Long <Waiman.Long@hp.com>
      Link: http://lkml.kernel.org/r/1430251224-5764-6-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      71107445
    • J
      sched, timer: Replace spinlocks with atomics in thread_group_cputimer(), to improve scalability · 1018016c
      Jason Low 提交于
      While running a database workload, we found a scalability issue with itimers.
      
      Much of the problem was caused by the thread_group_cputimer spinlock.
      Each time we account for group system/user time, we need to obtain a
      thread_group_cputimer's spinlock to update the timers. On larger systems
      (such as a 16 socket machine), this caused more than 30% of total time
      spent trying to obtain this kernel lock to update these group timer stats.
      
      This patch converts the timers to 64-bit atomic variables and use
      atomic add to update them without a lock. With this patch, the percent
      of total time spent updating thread group cputimer timers was reduced
      from 30% down to less than 1%.
      
      Note: On 32-bit systems using the generic 64-bit atomics, this causes
      sample_group_cputimer() to take locks 3 times instead of just 1 time.
      However, we tested this patch on a 32-bit system ARM system using the
      generic atomics and did not find the overhead to be much of an issue.
      An explanation for why this isn't an issue is that 32-bit systems usually
      have small numbers of CPUs, and cacheline contention from extra spinlocks
      called periodically is not really apparent on smaller systems.
      Signed-off-by: NJason Low <jason.low2@hp.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Acked-by: NThomas Gleixner <tglx@linutronix.de>
      Acked-by: NRik van Riel <riel@redhat.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Aswin Chandramouleeswaran <aswin@hp.com>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Davidlohr Bueso <dave@stgolabs.net>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
      Cc: Scott J Norton <scott.norton@hp.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Waiman Long <Waiman.Long@hp.com>
      Link: http://lkml.kernel.org/r/1430251224-5764-4-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      1018016c
    • J
      sched, timer: Convert usages of ACCESS_ONCE() in the scheduler to READ_ONCE()/WRITE_ONCE() · 316c1608
      Jason Low 提交于
      ACCESS_ONCE doesn't work reliably on non-scalar types. This patch removes
      the rest of the existing usages of ACCESS_ONCE() in the scheduler, and use
      the new READ_ONCE() and WRITE_ONCE() APIs as appropriate.
      Signed-off-by: NJason Low <jason.low2@hp.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Acked-by: NThomas Gleixner <tglx@linutronix.de>
      Acked-by: NRik van Riel <riel@redhat.com>
      Acked-by: NWaiman Long <Waiman.Long@hp.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Aswin Chandramouleeswaran <aswin@hp.com>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Davidlohr Bueso <dave@stgolabs.net>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
      Cc: Scott J Norton <scott.norton@hp.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Link: http://lkml.kernel.org/r/1430251224-5764-2-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      316c1608
  14. 13 2月, 2015 1 次提交
    • A
      all arches, signal: move restart_block to struct task_struct · f56141e3
      Andy Lutomirski 提交于
      If an attacker can cause a controlled kernel stack overflow, overwriting
      the restart block is a very juicy exploit target.  This is because the
      restart_block is held in the same memory allocation as the kernel stack.
      
      Moving the restart block to struct task_struct prevents this exploit by
      making the restart_block harder to locate.
      
      Note that there are other fields in thread_info that are also easy
      targets, at least on some architectures.
      
      It's also a decent simplification, since the restart code is more or less
      identical on all architectures.
      
      [james.hogan@imgtec.com: metag: align thread_info::supervisor_stack]
      Signed-off-by: NAndy Lutomirski <luto@amacapital.net>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: David Miller <davem@davemloft.net>
      Acked-by: NRichard Weinberger <richard@nod.at>
      Cc: Richard Henderson <rth@twiddle.net>
      Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
      Cc: Matt Turner <mattst88@gmail.com>
      Cc: Vineet Gupta <vgupta@synopsys.com>
      Cc: Russell King <rmk@arm.linux.org.uk>
      Cc: Catalin Marinas <catalin.marinas@arm.com>
      Cc: Will Deacon <will.deacon@arm.com>
      Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
      Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
      Cc: Steven Miao <realmz6@gmail.com>
      Cc: Mark Salter <msalter@redhat.com>
      Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
      Cc: Mikael Starvik <starvik@axis.com>
      Cc: Jesper Nilsson <jesper.nilsson@axis.com>
      Cc: David Howells <dhowells@redhat.com>
      Cc: Richard Kuo <rkuo@codeaurora.org>
      Cc: "Luck, Tony" <tony.luck@intel.com>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Michal Simek <monstr@monstr.eu>
      Cc: Ralf Baechle <ralf@linux-mips.org>
      Cc: Jonas Bonn <jonas@southpole.se>
      Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
      Cc: Helge Deller <deller@gmx.de>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Paul Mackerras <paulus@samba.org>
      Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
      Tested-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: Chen Liqin <liqin.linux@gmail.com>
      Cc: Lennox Wu <lennox.wu@gmail.com>
      Cc: Chris Metcalf <cmetcalf@ezchip.com>
      Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
      Cc: Chris Zankel <chris@zankel.net>
      Cc: Max Filippov <jcmvbkbc@gmail.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Guenter Roeck <linux@roeck-us.net>
      Signed-off-by: NJames Hogan <james.hogan@imgtec.com>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      f56141e3
  15. 16 11月, 2014 1 次提交
  16. 08 9月, 2014 1 次提交
    • R
      time, signal: Protect resource use statistics with seqlock · e78c3496
      Rik van Riel 提交于
      Both times() and clock_gettime(CLOCK_PROCESS_CPUTIME_ID) have scalability
      issues on large systems, due to both functions being serialized with a
      lock.
      
      The lock protects against reporting a wrong value, due to a thread in the
      task group exiting, its statistics reporting up to the signal struct, and
      that exited task's statistics being counted twice (or not at all).
      
      Protecting that with a lock results in times() and clock_gettime() being
      completely serialized on large systems.
      
      This can be fixed by using a seqlock around the events that gather and
      propagate statistics. As an additional benefit, the protection code can
      be moved into thread_group_cputime(), slightly simplifying the calling
      functions.
      
      In the case of posix_cpu_clock_get_task() things can be simplified a
      lot, because the calling function already ensures that the task sticks
      around, and the rest is now taken care of in thread_group_cputime().
      
      This way the statistics reporting code can run lockless.
      Signed-off-by: NRik van Riel <riel@redhat.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Alex Thorlton <athorlton@sgi.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Daeseok Youn <daeseok.youn@gmail.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Guillaume Morin <guillaume@morinfr.org>
      Cc: Ionut Alexa <ionut.m.alexa@gmail.com>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Li Zefan <lizefan@huawei.com>
      Cc: Michal Hocko <mhocko@suse.cz>
      Cc: Michal Schmidt <mschmidt@redhat.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Vladimir Davydov <vdavydov@parallels.com>
      Cc: umgwanakikbuti@gmail.com
      Cc: fweisbec@gmail.com
      Cc: srao@redhat.com
      Cc: lwoodman@redhat.com
      Cc: atheurer@redhat.com
      Link: http://lkml.kernel.org/r/20140816134010.26a9b572@annuminas.surriel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      e78c3496
  17. 23 6月, 2014 1 次提交
  18. 09 12月, 2013 10 次提交
    • F
      posix-timers: Convert abuses of BUG_ON to WARN_ON · 531f64fd
      Frederic Weisbecker 提交于
      The posix cpu timers code makes a heavy use of BUG_ON()
      but none of these concern fatal issues that require
      to stop the machine. So let's just warn the user when
      some internal state slips out of our hands.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      531f64fd
    • F
      posix-timers: Remove remaining uses of tasklist_lock · e73d84e3
      Frederic Weisbecker 提交于
      The remaining uses of tasklist_lock were mostly about synchronizing
      against sighand modifications, getting coherent and safe group samples
      and also thread/process wide timers list handling.
      
      All of this is already safely synchronizable with the target's
      sighand lock. Let's use it on these places instead.
      
      Also update the comments about locking.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      e73d84e3
    • F
      posix-timers: Use sighand lock instead of tasklist_lock on timer deletion · 3d7a1427
      Frederic Weisbecker 提交于
      Timer deletion doesn't need the tasklist lock.
      We need to protect against:
      
      * concurrent access to the lists p->cputime_expires and
        p->sighand->cputime_expires
      
      * task reaping that may also delete the timer list entry
      
      * timer firing
      
      We already hold the timer lock which protects us against concurrent
      timer firing.
      
      The rest only need the targets sighand to be locked.
      So hold it and drop the use of tasklist_lock there.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      3d7a1427
    • F
      posix-timers: Use sighand lock instead of tasklist_lock for task clock sample · 50875788
      Frederic Weisbecker 提交于
      There is no need for the tasklist_lock just to take a process
      wide clock sample.
      
      All we need is to get a coherent sample that doesn't race with
      exit() and exec():
      
      * exit() may be concurrently reaping a task and flushing its time
      
      * sighand is unstable under exit() and exec(), and the latter also
        result in group leader that can change
      
      To protect against these, locking the target's sighand is enough.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      50875788
    • F
      posix-timers: Consolidate posix_cpu_clock_get() · 33ab0fec
      Frederic Weisbecker 提交于
      Consolidate the clock sampling common code used for both local
      and remote targets.
      
      Note that this introduces a tiny user ABI change: if a
      PID is passed to clock_gettime() along the clockid,
      we used to forbid a process wide clock sample when that
      PID doesn't belong to a group leader. Now after this patch
      we allow process wide clock samples if that PID belongs to
      the current task, even if the current task is not the
      group leader.
      
      But local process wide clock samples are allowed if PID == 0
      (current task) even if the current task is not the group leader.
      So in the end this should be no big deal as this actually harmonize
      the behaviour when the remote sample is actually a local one.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      33ab0fec
    • F
      posix-timers: Remove useless clock sample on timers cleanup · af82eb3c
      Frederic Weisbecker 提交于
      a0b2062b
      ("posix_timers: fix racy timer delta caching on task exit") forgot
      to remove the arguments used for timer caching.
      
      Fix this leftover.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      af82eb3c
    • F
      posix-timers: Remove dead task special case · a3222f88
      Frederic Weisbecker 提交于
      Now that we've removed all the optimizations that could
      result in NULL timer's targets, we can remove all the
      associated special case handling.
      
      Also add some warnings on NULL targets to spot any possible
      leftover.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      a3222f88
    • F
      posix-timers: Cleanup reaped target handling · e26d70d2
      Frederic Weisbecker 提交于
      When a timer's target is seen to be buried, for example on calls
      to timer_gettime(), the posix cpu timers code behaves a bit
      like a garbage collector and releases early the reference to the
      task.
      
      Then again, this optimization complicates the code for no much
      value: it's up to the user to release the timer and its associated
      ressources by calling timer_delete() after it buries the target
      tasks.
      
      Remove this to simplify the code.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      e26d70d2
    • F
      posix-timers: Remove dead process posix cpu timers caching · d430b917
      Frederic Weisbecker 提交于
      Now that we removed dead thread posix cpu timers caching,
      lets remove the dead process wide version. This caching
      is similar to the per thread version but it should be even
      more rare:
      
      * If the process id dead, we are not reading its timers
      status from a thread belonging to its group since they
      are all dead. So this caching only concern remote process
      timers reads. Now posix cpu timers using itimers or timer_settime()
      can't do remote process timers anyway so it's not even clear if there
      is actually a user for this caching.
      
      * Unlike per thread timers caching, this only applies to
      zombies targets. Buried targets' process wide timers return
      0 values. But then again, timer_gettime() can't read remote
      process timers, so if the process is dead, there can't be
      any reader left anyway.
      
      Then again this caching seem to complicate the code for
      corner cases that are probably not worth it. So lets get
      rid of it.
      
      Also remove the sample snapshot on dying process timer
      that is now useless, as suggested by Kosaki.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      d430b917
    • F
      posix-timers: Remove dead thread posix cpu timers caching · 724a3713
      Frederic Weisbecker 提交于
      When a task is exiting or has exited, its posix cpu timers
      don't tick anymore and won't elapse further. It's too late
      for them to expire.
      
      So any further call to timer_gettime() on these timers will
      return the same remaining expiry time.
      
      The current code optimize this by caching the remaining delta
      and storing it where we use to save the absolute expiration time.
      This way, the future calls to timer_gettime() won't need to
      compute the difference between the absolute expiration time and
      the current time anymore.
      
      Now this optimization doesn't seem to bring much value. Computing
      the timer remaining delta is not very costly. Fetching the timer
      value OTOH can be costly in two ways:
      
      * CPUCLOCK_SCHED read requires to lock the target's rq. But some
      optimizations are on the way to make task_sched_runtime() not holding
      the rq lock of a non-running target.
      
      * CPUCLOCK_VIRT/CPUCLOCK_PROF read simply consist in fetching
      current->utime/current->stime except when the system uses full
      dynticks cputime accounting. The latter requires a per task lock
      in order to correctly compute user and system time. But once the
      target is dead, this lock shouldn't be contended anyway.
      
      All in one this caching doesn't seem to be justified.
      Given that it complicates the code significantly for
      few wins, let's remove it on single thread timers.
      Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      724a3713