1. 27 5月, 2011 1 次提交
  2. 23 5月, 2011 1 次提交
    • L
      Give up on pushing CC_OPTIMIZE_FOR_SIZE · 281dc5c5
      Linus Torvalds 提交于
      I still happen to believe that I$ miss costs are a major thing, but
      sadly, -Os doesn't seem to be the solution.  With or without it, gcc
      will miss some obvious code size improvements, and with it enabled gcc
      will sometimes make choices that aren't good even with high I$ miss
      ratios.
      
      For example, with -Os, gcc on x86 will turn a 20-byte constant memcpy
      into a "rep movsl".  While I sincerely hope that x86 CPU's will some day
      do a good job at that, they certainly don't do it yet, and the cost is
      higher than a L1 I$ miss would be.
      
      Some day I hope we can re-enable this.
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      281dc5c5
  3. 21 5月, 2011 1 次提交
  4. 11 5月, 2011 1 次提交
  5. 06 5月, 2011 1 次提交
  6. 27 4月, 2011 1 次提交
    • R
      init/Kconfig: fix EXPERT menu list · 6befe5f6
      Randy Dunlap 提交于
      The EXPERT menu list was recently broken by the insertion of a
      kconfig symbol (EMBEDDED) at the beginning of the EXPERT list of
      kconfig items.  Broken by:
      
        commit 6a108a14
        Author: David Rientjes <rientjes@google.com>
        Date:   Thu Jan 20 14:44:16 2011 -0800
          kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT
      
      Restore the EXPERT menu list -- don't inject a symbol (EMBEDDED)
      that does not depend on EXPERT into the list.
      Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
      Cc: David Rientjes <rientjes@google.com>
      Cc: Peter Foley <pefoley2@verizon.net>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6befe5f6
  7. 23 4月, 2011 1 次提交
    • J
      [PARISC] slub: fix panic with DISCONTIGMEM · 4a5fa359
      James Bottomley 提交于
      Slub makes assumptions about page_to_nid() which are violated by
      DISCONTIGMEM and !NUMA.  This violation results in a panic because
      page_to_nid() can be non-zero for pages in the discontiguous ranges and
      this leads to a null return by get_node().  The assertion by the
      maintainer is that DISCONTIGMEM should only be allowed when NUMA is also
      defined.  However, at least six architectures: alpha, ia64, m32r, m68k,
      mips, parisc violate this.  The panic is a regression against slab, so
      just mark slub broken in the problem configuration to prevent users
      reporting these panics.
      
      Cc: stable@kernel.org
      Acked-by: NDavid Rientjes <rientjes@google.com>
      Acked-by: NPekka Enberg <penberg@kernel.org>
      Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>
      4a5fa359
  8. 15 4月, 2011 2 次提交
    • A
      kbuild: move KALLSYMS_EXTRA_PASS from Kconfig to Makefile · 1e2795a1
      Artem Bityutskiy 提交于
      At the moment we have the CONFIG_KALLSYMS_EXTRA_PASS Kconfig switch,
      which users can enable or disable while configuring the kernel. This
      option is then used by 'make' to determine whether an extra kallsyms
      pass is needed or not.
      
      However, this approach is not nice and confusing, and this patch moves
      CONFIG_KALLSYMS_EXTRA_PASS from Kconfig to Makefile instead. The
      rationale is below.
      
      1. CONFIG_KALLSYMS_EXTRA_PASS is really about the build time, not
         run-time. There is no real need for it to be in Kconfig. It is
         just an additional work-around which should be used only in rare
         cases, when someone breaks kallsyms, so Kbuild/Makefile is much
         better place for this option.
      2. Grepping CONFIG_KALLSYMS_EXTRA_PASS shows that many defconfigs have
         it enabled, probably not because they try to work-around a kallsyms
         bug, but just because the Kconfig help text is confusing and does
         not really make it clear that this option should not be used unless
         except when kallsyms is broken.
      3. And since many people have CONFIG_KALLSYMS_EXTRA_PASS enabled in
         their Kconfig, we do might fail to notice kallsyms bugs in time. E.g.,
         many testers use "make allyesconfig" to test builds, which will enable
         CONFIG_KALLSYMS_EXTRA_PASS and kallsyms breakage will not be noticed.
      
      To address that, this patch:
      
      1. Kills CONFIG_KALLSYMS_EXTRA_PASS
      2. Changes Makefile so that people can use "make KALLSYMS_EXTRA_PASS=1"
         to enable the extra pass if needed. Additionally, they may define
         KALLSYMS_EXTRA_PASS as an environment variable.
      3. By default KALLSYMS_EXTRA_PASS is disabled and if kallsyms has issues,
         "make" should print a warning and suggest using KALLSYMS_EXTRA_PASS
      Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
      [mmarek: Removed make help text, is not necessary]
      Signed-off-by: NMichal Marek <mmarek@suse.cz>
      1e2795a1
    • A
      Kconfig: improve KALLSYMS_ALL documentation · 71a83ec7
      Artem Bityutskiy 提交于
      Dumb users like myself are not able to grasp from the existing KALLSYMS_ALL
      documentation that this option is not what they need. Improve the help
      message and make it clearer that KALLSYMS is enough in the majority of
      use cases, and KALLSYMS_ALL should really be used very rarely.
      Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
      Signed-off-by: NMichal Marek <mmarek@suse.cz>
      71a83ec7
  9. 14 4月, 2011 1 次提交
  10. 15 3月, 2011 1 次提交
  11. 05 3月, 2011 1 次提交
    • A
      BKL: That's all, folks · 4ba8216c
      Arnd Bergmann 提交于
      This removes the implementation of the big kernel lock,
      at last. A lot of people have worked on this in the
      past, I so the credit for this patch should be with
      everyone who participated in the hunt.
      
      The names on the Cc list are the people that were the
      most active in this, according to the recorded git
      history, in alphabetical order.
      Signed-off-by: NArnd Bergmann <arnd@arndb.de>
      Acked-by: NAlan Cox <alan@linux.intel.com>
      Cc: Alessio Igor Bogani <abogani@texware.it>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: Andrew Hendry <andrew.hendry@gmail.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Christoph Hellwig <hch@infradead.org>
      Cc: Eric W. Biederman <ebiederm@xmission.com>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Cc: Hans Verkuil <hverkuil@xs4all.nl>
      Acked-by: NIngo Molnar <mingo@elte.hu>
      Cc: Jan Blunck <jblunck@infradead.org>
      Cc: John Kacur <jkacur@redhat.com>
      Cc: Jonathan Corbet <corbet@lwn.net>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Matthew Wilcox <matthew@wil.cx>
      Cc: Oliver Neukum <oliver@neukum.org>
      Cc: Paul Menage <menage@google.com>
      Acked-by: NThomas Gleixner <tglx@linutronix.de>
      Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
      4ba8216c
  12. 04 3月, 2011 1 次提交
  13. 16 2月, 2011 1 次提交
    • S
      perf: Add cgroup support · e5d1367f
      Stephane Eranian 提交于
      This kernel patch adds the ability to filter monitoring based on
      container groups (cgroups). This is for use in per-cpu mode only.
      
      The cgroup to monitor is passed as a file descriptor in the pid
      argument to the syscall. The file descriptor must be opened to
      the cgroup name in the cgroup filesystem. For instance, if the
      cgroup name is foo and cgroupfs is mounted in /cgroup, then the
      file descriptor is opened to /cgroup/foo. Cgroup mode is
      activated by passing PERF_FLAG_PID_CGROUP in the flags argument
      to the syscall.
      
      For instance to measure in cgroup foo on CPU1 assuming
      cgroupfs is mounted under /cgroup:
      
      struct perf_event_attr attr;
      int cgroup_fd, fd;
      
      cgroup_fd = open("/cgroup/foo", O_RDONLY);
      fd = perf_event_open(&attr, cgroup_fd, 1, -1, PERF_FLAG_PID_CGROUP);
      close(cgroup_fd);
      Signed-off-by: NStephane Eranian <eranian@google.com>
      [ added perf_cgroup_{exit,attach} ]
      Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      LKML-Reference: <4d590250.114ddf0a.689e.4482@mx.google.com>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e5d1367f
  14. 04 2月, 2011 1 次提交
  15. 21 1月, 2011 1 次提交
    • D
      kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT · 6a108a14
      David Rientjes 提交于
      The meaning of CONFIG_EMBEDDED has long since been obsoleted; the option
      is used to configure any non-standard kernel with a much larger scope than
      only small devices.
      
      This patch renames the option to CONFIG_EXPERT in init/Kconfig and fixes
      references to the option throughout the kernel.  A new CONFIG_EMBEDDED
      option is added that automatically selects CONFIG_EXPERT when enabled and
      can be used in the future to isolate options that should only be
      considered for embedded systems (RISC architectures, SLOB, etc).
      
      Calling the option "EXPERT" more accurately represents its intention: only
      expert users who understand the impact of the configuration changes they
      are making should enable it.
      Reviewed-by: NIngo Molnar <mingo@elte.hu>
      Acked-by: NDavid Woodhouse <david.woodhouse@intel.com>
      Signed-off-by: NDavid Rientjes <rientjes@google.com>
      Cc: Greg KH <gregkh@suse.de>
      Cc: "David S. Miller" <davem@davemloft.net>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Arnd Bergmann <arnd@arndb.de>
      Cc: Robin Holt <holt@sgi.com>
      Cc: <linux-arch@vger.kernel.org>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6a108a14
  16. 17 1月, 2011 2 次提交
  17. 14 1月, 2011 2 次提交
    • P
      rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status · c072a388
      Paul E. McKenney 提交于
      Because the adaptive synchronize_srcu_expedited() approach has
      worked very well in testing, remove the kernel parameter and
      replace it by a C-preprocessor macro.  If someone finds problems
      with this approach, a more complex and aggressively adaptive
      approach might be required.
      
      Longer term, SRCU will be merged with the other RCU implementations,
      at which point synchronize_srcu_expedited() will be event driven,
      just as synchronize_sched_expedited() currently is.  At that point,
      there will be no need for this adaptive approach.
      Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      c072a388
    • L
      decompressors: add boot-time XZ support · 3ebe1243
      Lasse Collin 提交于
      This implements the API defined in <linux/decompress/generic.h> which is
      used for kernel, initramfs, and initrd decompression.  This patch together
      with the first patch is enough for XZ-compressed initramfs and initrd;
      XZ-compressed kernel will need arch-specific changes.
      
      The buffering requirements described in decompress_unxz.c are stricter
      than with gzip, so the relevant changes should be done to the
      arch-specific code when adding support for XZ-compressed kernel.
      Similarly, the heap size in arch-specific pre-boot code may need to be
      increased (30 KiB is enough).
      
      The XZ decompressor needs memmove(), memeq() (memcmp() == 0), and
      memzero() (memset(ptr, 0, size)), which aren't available in all
      arch-specific pre-boot environments.  I'm including simple versions in
      decompress_unxz.c, but a cleaner solution would naturally be nicer.
      Signed-off-by: NLasse Collin <lasse.collin@tukaani.org>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Alain Knaff <alain@knaff.lu>
      Cc: Albin Tonnerre <albin.tonnerre@free-electrons.com>
      Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3ebe1243
  18. 23 12月, 2010 1 次提交
  19. 30 11月, 2010 4 次提交
    • M
      sched: Add 'autogroup' scheduling feature: automated per session task groups · 5091faa4
      Mike Galbraith 提交于
      A recurring complaint from CFS users is that parallel kbuild has
      a negative impact on desktop interactivity.  This patch
      implements an idea from Linus, to automatically create task
      groups.  Currently, only per session autogroups are implemented,
      but the patch leaves the way open for enhancement.
      
      Implementation: each task's signal struct contains an inherited
      pointer to a refcounted autogroup struct containing a task group
      pointer, the default for all tasks pointing to the
      init_task_group.  When a task calls setsid(), a new task group
      is created, the process is moved into the new task group, and a
      reference to the preveious task group is dropped.  Child
      processes inherit this task group thereafter, and increase it's
      refcount.  When the last thread of a process exits, the
      process's reference is dropped, such that when the last process
      referencing an autogroup exits, the autogroup is destroyed.
      
      At runqueue selection time, IFF a task has no cgroup assignment,
      its current autogroup is used.
      
      Autogroup bandwidth is controllable via setting it's nice level
      through the proc filesystem:
      
        cat /proc/<pid>/autogroup
      
      Displays the task's group and the group's nice level.
      
        echo <nice level> > /proc/<pid>/autogroup
      
      Sets the task group's shares to the weight of nice <level> task.
      Setting nice level is rate limited for !admin users due to the
      abuse risk of task group locking.
      
      The feature is enabled from boot by default if
      CONFIG_SCHED_AUTOGROUP=y is selected, but can be disabled via
      the boot option noautogroup, and can also be turned on/off on
      the fly via:
      
        echo [01] > /proc/sys/kernel/sched_autogroup_enabled
      
      ... which will automatically move tasks to/from the root task group.
      Signed-off-by: NMike Galbraith <efault@gmx.de>
      Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
      Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
      Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
      Cc: Paul Turner <pjt@google.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      [ Removed the task_group_path() debug code, and fixed !EVENTFD build failure. ]
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      LKML-Reference: <1290281700.28711.9.camel@maggy.simson.net>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      5091faa4
    • P
      rcu: Make synchronize_srcu_expedited() fast if running readers · 46fdb093
      Paul E. McKenney 提交于
      The synchronize_srcu_expedited() function is currently quick if there
      are no active readers, but will delay a full jiffy if there are any.
      If these readers leave their SRCU read-side critical sections quickly,
      this is way too long to wait.  So this commit first waits ten microseconds,
      and only then falls back to jiffy-at-a-time waiting.
      Reported-by: NAvi Kivity <avi@redhat.com>
      Reported-by: NMarcelo Tosatti <mtosatti@redhat.com>
      Tested-by: NTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      46fdb093
    • P
      rcu: add tracing for TINY_RCU and TINY_PREEMPT_RCU · 9e571a82
      Paul E. McKenney 提交于
      Add tracing for the tiny RCU implementations, including statistics on
      boosting in the case of TINY_PREEMPT_RCU and RCU_BOOST.
      Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      9e571a82
    • P
      rcu: priority boosting for TINY_PREEMPT_RCU · 24278d14
      Paul E. McKenney 提交于
      Add priority boosting, but only for TINY_PREEMPT_RCU.  This is enabled
      by the default-off RCU_BOOST kernel parameter.  The priority to which to
      boost preempted RCU readers is controlled by the RCU_BOOST_PRIO kernel
      parameter (defaulting to real-time priority 1) and the time to wait
      before boosting the readers blocking a given grace period is controlled
      by the RCU_BOOST_DELAY kernel parameter (defaulting to 500 milliseconds).
      Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      24278d14
  20. 25 11月, 2010 1 次提交
    • M
      cgroups: make swap accounting default behavior configurable · a42c390c
      Michal Hocko 提交于
      Swap accounting can be configured by CONFIG_CGROUP_MEM_RES_CTLR_SWAP
      configuration option and then it is turned on by default.  There is a boot
      option (noswapaccount) which can disable this feature.
      
      This makes it hard for distributors to enable the configuration option as
      this feature leads to a bigger memory consumption and this is a no-go for
      general purpose distribution kernel.  On the other hand swap accounting
      may be very usuful for some workloads.
      
      This patch adds a new configuration option which controls the default
      behavior (CGROUP_MEM_RES_CTLR_SWAP_ENABLED).  If the option is selected
      then the feature is turned on by default.
      
      It also adds a new boot parameter swapaccount[=1|0] which enhances the
      original noswapaccount parameter semantic by means of enable/disable logic
      (defaults to 1 if no value is provided to be still consistent with
      noswapaccount).
      
      The default behavior is unchanged (if CONFIG_CGROUP_MEM_RES_CTLR_SWAP is
      enabled then CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED is enabled as well)
      Signed-off-by: NMichal Hocko <mhocko@suse.cz>
      Acked-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
      Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
      Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a42c390c
  21. 28 10月, 2010 6 次提交
  22. 23 10月, 2010 2 次提交
    • A
      SYSFS: Allow boot time switching between deprecated and modern sysfs layout · e52eec13
      Andi Kleen 提交于
      I have some systems which need legacy sysfs due to old tools that are
      making assumptions that a directory can never be a symlink to another
      directory, and it's a big hazzle to compile separate kernels for them.
      
      This patch turns CONFIG_SYSFS_DEPRECATED into a run time option
      that can be switched on/off the kernel command line. This way
      the same binary can be used in both cases with just a option
      on the command line.
      
      The old CONFIG_SYSFS_DEPRECATED_V2 option is still there to set
      the default. I kept the weird name to not break existing
      config files.
      
      Also the compat code can be still completely disabled by undefining
      CONFIG_SYSFS_DEPRECATED_SWITCH -- just the optimizer takes
      care of this now instead of lots of ifdefs. This makes the code
      look nicer.
      
      v2: This is an updated version on top of Kay's patch to only
      handle the block devices. I tested it on my old systems
      and that seems to work.
      
      Cc: axboe@kernel.dk
      Signed-off-by: NAndi Kleen <ak@linux.intel.com>
      Cc: Kay Sievers <kay.sievers@vrfy.org>
      Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
      e52eec13
    • K
      driver core: remove CONFIG_SYSFS_DEPRECATED_V2 but keep it for block devices · 39aba963
      Kay Sievers 提交于
      This patch removes the old CONFIG_SYSFS_DEPRECATED_V2 config option,
      but it keeps the logic around to handle block devices in the old manner
      as some people like to run new kernel versions on old (pre 2007/2008)
      distros.
      Signed-off-by: NKay Sievers <kay.sievers@vrfy.org>
      Cc: Jens Axboe <axboe@kernel.dk>
      Cc: Stephen Hemminger <shemminger@vyatta.com>
      Cc: "Eric W. Biederman" <ebiederm@xmission.com>
      Cc: Alan Stern <stern@rowland.harvard.edu>
      Cc: "James E.J. Bottomley" <James.Bottomley@suse.de>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
      Cc: Randy Dunlap <randy.dunlap@oracle.com>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: "David S. Miller" <davem@davemloft.net>
      Cc: Jaroslav Kysela <perex@perex.cz>
      Cc: Takashi Iwai <tiwai@suse.de>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: David Howells <dhowells@redhat.com>
      Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
      
      39aba963
  23. 21 10月, 2010 1 次提交
    • A
      BKL: introduce CONFIG_BKL. · 6de5bd12
      Arnd Bergmann 提交于
      With all the patches we have queued in the BKL removal tree, only a
      few dozen modules are left that actually rely on the BKL, and even
      there are lots of low-hanging fruit. We need to decide what to do
      about them, this patch illustrates one of the options:
      
      Every user of the BKL is marked as 'depends on BKL' in Kconfig,
      and the CONFIG_BKL becomes a user-visible option. If it gets
      disabled, no BKL using module can be built any more and the BKL
      code itself is compiled out.
      
      The one exception is file locking, which is practically always
      enabled and does a 'select BKL' instead. This effectively forces
      CONFIG_BKL to be enabled until we have solved the fs/lockd
      mess and can apply the patch that removes the BKL from fs/locks.c.
      Signed-off-by: NArnd Bergmann <arnd@arndb.de>
      6de5bd12
  24. 19 10月, 2010 1 次提交
    • P
      irq_work: Add generic hardirq context callbacks · e360adbe
      Peter Zijlstra 提交于
      Provide a mechanism that allows running code in IRQ context. It is
      most useful for NMI code that needs to interact with the rest of the
      system -- like wakeup a task to drain buffers.
      
      Perf currently has such a mechanism, so extract that and provide it as
      a generic feature, independent of perf so that others may also
      benefit.
      
      The IRQ context callback is generated through self-IPIs where
      possible, or on architectures like powerpc the decrementer (the
      built-in timer facility) is set to generate an interrupt immediately.
      
      Architectures that don't have anything like this get to do with a
      callback from the timer tick. These architectures can call
      irq_work_run() at the tail of any IRQ handlers that might enqueue such
      work (like the perf IRQ handler) to avoid undue latencies in
      processing the work.
      Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      Acked-by: NKyle McMartin <kyle@mcmartin.ca>
      Acked-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
      [ various fixes ]
      Signed-off-by: NHuang Ying <ying.huang@intel.com>
      LKML-Reference: <1287036094.7768.291.camel@yhuang-dev>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e360adbe
  25. 04 10月, 2010 1 次提交
  26. 16 9月, 2010 1 次提交
  27. 23 8月, 2010 1 次提交
  28. 20 8月, 2010 1 次提交
    • P
      rcu: Add a TINY_PREEMPT_RCU · a57eb940
      Paul E. McKenney 提交于
      Implement a small-memory-footprint uniprocessor-only implementation of
      preemptible RCU.  This implementation uses but a single blocked-tasks
      list rather than the combinatorial number used per leaf rcu_node by
      TREE_PREEMPT_RCU, which reduces memory consumption and greatly simplifies
      processing.  This version also takes advantage of uniprocessor execution
      to accelerate grace periods in the case where there are no readers.
      
      The general design is otherwise broadly similar to that of TREE_PREEMPT_RCU.
      
      This implementation is a step towards having RCU implementation driven
      off of the SMP and PREEMPT kernel configuration variables, which can
      happen once this implementation has accumulated sufficient experience.
      
      Removed ACCESS_ONCE() from __rcu_read_unlock() and added barrier() as
      suggested by Steve Rostedt in order to avoid the compiler-reordering
      issue noted by Mathieu Desnoyers (http://lkml.org/lkml/2010/8/16/183).
      
      As can be seen below, CONFIG_TINY_PREEMPT_RCU represents almost 5Kbyte
      savings compared to CONFIG_TREE_PREEMPT_RCU.  Of course, for non-real-time
      workloads, CONFIG_TINY_RCU is even better.
      
      	CONFIG_TREE_PREEMPT_RCU
      
      	   text	   data	    bss	    dec	   filename
      	     13	      0	      0	     13	   kernel/rcupdate.o
      	   6170	    825	     28	   7023	   kernel/rcutree.o
      				   ----
      				   7026    Total
      
      	CONFIG_TINY_PREEMPT_RCU
      
      	   text	   data	    bss	    dec	   filename
      	     13	      0	      0	     13	   kernel/rcupdate.o
      	   2081	     81	      8	   2170	   kernel/rcutiny.o
      				   ----
      				   2183    Total
      
      	CONFIG_TINY_RCU (non-preemptible)
      
      	   text	   data	    bss	    dec	   filename
      	     13	      0	      0	     13	   kernel/rcupdate.o
      	    719	     25	      0	    744	   kernel/rcutiny.o
      				    ---
      				    757    Total
      Requested-by: NLoïc Minier <loic.minier@canonical.com>
      Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      a57eb940