locking/pvqspinlock: Collect slowpath lock statistics
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: Waiman Long <Waiman.Long@hpe.com>
Signed-off-by: Peter 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.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
3 files changed