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  1. 02 3月, 2017 1 次提交
  3. 05 12月, 2016 1 次提交
  5. 10 8月, 2016 2 次提交
  7. 05 5月, 2016 2 次提交
  9. 19 4月, 2016 1 次提交
    • D
      locking/pvqspinlock: Fix division by zero in qstat_read() · 66876595
      由 Davidlohr Bueso 提交于 
      While playing with the qstat statistics (in <debugfs>/qlockstat/) I ran into
the following splat on a VM when opening pv_hash_hops:

  divide error: 0000 [#1] SMP
  ...
  RIP: 0010:[<ffffffff810b61fe>]  [<ffffffff810b61fe>] qstat_read+0x12e/0x1e0
  ...
  Call Trace:
    [<ffffffff811cad7c>] ? mem_cgroup_commit_charge+0x6c/0xd0
    [<ffffffff8119750c>] ? page_add_new_anon_rmap+0x8c/0xd0
    [<ffffffff8118d3b9>] ? handle_mm_fault+0x1439/0x1b40
    [<ffffffff811937a9>] ? do_mmap+0x449/0x550
    [<ffffffff811d3de3>] ? __vfs_read+0x23/0xd0
    [<ffffffff811d4ab2>] ? rw_verify_area+0x52/0xd0
    [<ffffffff811d4bb1>] ? vfs_read+0x81/0x120
    [<ffffffff811d5f12>] ? SyS_read+0x42/0xa0
    [<ffffffff815720f6>] ? entry_SYSCALL_64_fastpath+0x1e/0xa8

Fix this by verifying that qstat_pv_kick_unlock is in fact non-zero,
similarly to what the qstat_pv_latency_wake case does, as if nothing
else, this can come from resetting the statistics, thus having 0 kicks
should be quite valid in this context.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Reviewed-by: NWaiman Long <Waiman.Long@hpe.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: waiman.long@hpe.com
Link: http://lkml.kernel.org/r/1460961103-24953-1-git-send-email-dave@stgolabs.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      66876595
  11. 29 2月, 2016 2 次提交
  13. 04 12月, 2015 3 次提交
    • W
      locking/pvqspinlock: Queue node adaptive spinning · cd0272fa
      由 Waiman Long 提交于 
      In an overcommitted guest where some vCPUs have to be halted to make
forward progress in other areas, it is highly likely that a vCPU later
in the spinlock queue will be spinning while the ones earlier in the
queue would have been halted. The spinning in the later vCPUs is then
just a waste of precious CPU cycles because they are not going to
get the lock soon as the earlier ones have to be woken up and take
their turn to get the lock.

This patch implements an adaptive spinning mechanism where the vCPU
will call pv_wait() if the previous vCPU is not running.

Linux kernel builds were run in KVM guest on an 8-socket, 4
cores/socket Westmere-EX system and a 4-socket, 8 cores/socket
Haswell-EX system. Both systems are configured to have 32 physical
CPUs. The kernel build times before and after the patch were:

		    Westmere			Haswell
  Patch		32 vCPUs    48 vCPUs	32 vCPUs    48 vCPUs
  -----		--------    --------    --------    --------
  Before patch   3m02.3s     5m00.2s     1m43.7s     3m03.5s
  After patch    3m03.0s     4m37.5s	 1m43.0s     2m47.2s

For 32 vCPUs, this patch doesn't cause any noticeable change in
performance. For 48 vCPUs (over-committed), there is about 8%
performance improvement.
Signed-off-by: NWaiman Long <Waiman.Long@hpe.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Douglas Hatch <doug.hatch@hpe.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447114167-47185-8-git-send-email-Waiman.Long@hpe.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      cd0272fa
    • W
      locking/pvqspinlock: Allow limited lock stealing · 1c4941fd
      由 Waiman Long 提交于 
      This patch allows one attempt for the lock waiter to steal the lock
when entering the PV slowpath. To prevent lock starvation, the pending
bit will be set by the queue head vCPU when it is in the active lock
spinning loop to disable any lock stealing attempt.  This helps to
reduce the performance penalty caused by lock waiter preemption while
not having much of the downsides of a real unfair lock.

The pv_wait_head() function was renamed as pv_wait_head_or_lock()
as it was modified to acquire the lock before returning. This is
necessary because of possible lock stealing attempts from other tasks.

Linux kernel builds were run in KVM guest on an 8-socket, 4
cores/socket Westmere-EX system and a 4-socket, 8 cores/socket
Haswell-EX system. Both systems are configured to have 32 physical
CPUs. The kernel build times before and after the patch were:

                    Westmere                    Haswell
  Patch         32 vCPUs    48 vCPUs    32 vCPUs    48 vCPUs
  -----         --------    --------    --------    --------
  Before patch   3m15.6s    10m56.1s     1m44.1s     5m29.1s
  After patch    3m02.3s     5m00.2s     1m43.7s     3m03.5s

For the overcommited case (48 vCPUs), this patch is able to reduce
kernel build time by more than 54% for Westmere and 44% for Haswell.
Signed-off-by: NWaiman Long <Waiman.Long@hpe.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Douglas Hatch <doug.hatch@hpe.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447190336-53317-1-git-send-email-Waiman.Long@hpe.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      1c4941fd
    • W
      locking/pvqspinlock: Collect slowpath lock statistics · 45e898b7
      由 Waiman Long 提交于 
      This patch enables the accumulation of kicking and waiting related
PV qspinlock statistics when the new QUEUED_LOCK_STAT configuration
option is selected. It also enables the collection of data which
enable us to calculate the kicking and wakeup latencies which have
a heavy dependency on the CPUs being used.

The statistical counters are per-cpu variables to minimize the
performance overhead in their updates. These counters are exported
via the debugfs filesystem under the qlockstat directory.  When the
corresponding debugfs files are read, summation and computing of the
required data are then performed.

The measured latencies for different CPUs are:

	CPU		Wakeup		Kicking
	---		------		-------
	Haswell-EX	63.6us		 7.4us
	Westmere-EX	67.6us		 9.3us

The measured latencies varied a bit from run-to-run. The wakeup
latency is much higher than the kicking latency.

A sample of statistical counters after system bootup (with vCPU
overcommit) was:

	pv_hash_hops=1.00
	pv_kick_unlock=1148
	pv_kick_wake=1146
	pv_latency_kick=11040
	pv_latency_wake=194840
	pv_spurious_wakeup=7
	pv_wait_again=4
	pv_wait_head=23
	pv_wait_node=1129
Signed-off-by: NWaiman Long <Waiman.Long@hpe.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Douglas Hatch <doug.hatch@hpe.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447114167-47185-6-git-send-email-Waiman.Long@hpe.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      45e898b7