Re: [PATCH RFC 00/16] A new RCU implementation based on a fast consensus protocol

From: Paul E. McKenney
Date: Sat Jan 27 2018 - 18:47:19 EST

On Sat, Jan 27, 2018 at 09:57:03AM +0000, Lihao Liang wrote:
> On Sat, Jan 27, 2018 at 7:57 AM, Paul E. McKenney
> <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > On Sat, Jan 27, 2018 at 07:22:27AM +0000, Lihao Liang wrote:
> >> On Thu, Jan 25, 2018 at 5:53 AM, Paul E. McKenney
> >> <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> >> > On Tue, Jan 23, 2018 at 03:59:25PM +0800, lianglihao@xxxxxxxxxx wrote:
> >> >> From: Lihao Liang <lianglihao@xxxxxxxxxx>
> >> >>
> >> >> Dear Paul,
> >> >>
> >> >> This patch set implements a preemptive version of RCU (PRCU) based on the following paper:
> >> >>
> >> >> Fast Consensus Using Bounded Staleness for Scalable Read-mostly Synchronization.
> >> >> Haibo Chen, Heng Zhang, Ran Liu, Binyu Zang, and Haibing Guan.
> >> >> IEEE Transactions on Parallel and Distributed Systems (TPDS), 2016.
> >> >> https://dl.acm.org/citation.cfm?id=3024114.3024143
> >> >>
> >> >> We have also added preliminary callback-handling support. Thus, the current version
> >> >> provides APIs prcu_read_lock(), prcu_read_unlock(), synchronize_prcu(), call_prcu(),
> >> >> and prcu_barrier().
> >> >>
> >> >> This is an experimental patch, so it would be good to have some feedback.
> >> >>
> >> >> Known shortcoming is that the grace-period version is incremented in synchronize_prcu().
> >> >> If call_prcu() or prcu_barrier() is called but there is no synchronized_prcu() invoked,
> >> >> callbacks cannot be invoked. Later version should address this issue, e.g. adding a
> >> >> grace-period expedition mechanism. Others include to use a a hierarchical structure,
> >> >> taking into account the NUMA topology, to send IPI in synchronize_prcu().
> >> >>
> >> >> We have tested the implementation using rcutorture on both an x86 and ARM64 machine.
> >> >> PRCU passed 1h and 3h tests on all the newly added config files except PRCU07 reported BUG
> >> >> in a 1h run.
> >> >>
> >> >> [ 1593.604201] ---[ end trace b3bae911bec86152 ]---
> >> >> [ 1594.629450] prcu-torture:torture_onoff task: offlining 14
> >> >> [ 1594.755553] smpboot: CPU 14 is now offline
> >> >> [ 1594.757732] prcu-torture:torture_onoff task: offlined 14
> >> >> [ 1597.765149] prcu-torture:torture_onoff task: onlining 11
> >> >> [ 1597.766795] smpboot: Booting Node 0 Processor 11 APIC 0xb
> >> >> [ 1597.804102] prcu-torture:torture_onoff task: onlined 11
> >> >> [ 1599.365098] prcu-torture: rtc: ffffffffb0277b90 ver: 66358 tfle: 0 rta: 66358 rtaf: 0
> >> >> rtf: 66349 rtmbe: 0 rtbe: 1 rtbke: 0 rtbre: 0 rtbf: 0 rtb: 0 nt: 2233418
> >> >> onoff: 191/191:199/199 34,199:59,5102 10403:0 (HZ=1000) barrier: 188/189:1 cbflood: 225
> >> >> [ 1599.367946] prcu-torture: !!!
> >> >> [ 1599.367966] ------------[ cut here ]------------
> >> >
> >> > The "rtbe: 1" indicates that your implementation of prcu_barrier()
> >> > failed to wait for all preceding call_prcu() callbacks to be invoked.
> >> >
> >> > Does the immediately following "Reader Pipe:" list have any but the
> >> > first two numbers non-zero?
> >>
> >> Yes.
> >
> > If the third or subsequent numbers are non-zero, that would indicate
> > too-short grace periods. This would be a critical bug in PRCU.
> >
> >> >> We have also compared PRCU with TREE RCU using rcuperf with gp_exp set to true, that is
> >> >> synchronize_rcu_expedited was tested.
> >> >>
> >> >> The rcuperf results are as follows (average grace-period duration in ms of ten 10min runs):
> >> >>
> >> >> 16*Intel Xeon CPU@xxxxxx, 16GB memory, Ubuntu Linux 3.13.0-47-generic
> >> >>
> >> >> CPUs 2 4 8 12 15 16
> >> >> PRCU 0.14 1.07 4.15 8.02 10.79 15.16
> >> >> TREE 49.30 104.75 277.55 390.82 620.82 1381.54
> >> >>
> >> >> 64*Cortex-A72 CPU@xxxxxx, 130GB memory, Ubuntu Linux 4.10.0-21.23-generic
> >> >>
> >> >> CPUs 2 4 8 16 32 48 63 64
> >> >> PRCU 0.23 19.69 38.28 63.21 95.41 167.18 252.01 1841.44
> >> >> TREE 416.73 901.89 1060.86 743.00 920.66 1325.21 1646.20 23806.27
> >> >
> >> > Well, at the very least, this is a bug report on either expedited RCU
> >> > grace-period latency or on rcuperf's measurements, and thank you for that.
> >> > I will look into this. In the meantime, could you please let me know
> >> > exactly how you invoked rcuperf?
> >>
> >> We used the following command to invoke rcuperf:
> >>
> >> sudo ./kvm.sh --torture rcuperf --duration 10 --configs 10*TREE
> >>
> >> The actual script run-rcuperf.sh to run the experiments can be found
> >> in the following email of this patch series:
> >>
> >> [PATCH RFC 15/16] rcutorture: Add scripts to run experiments
> >>
> >> Please let us know how it goes.
> >
> > Will do!
> >
> > As I said before, at the very least you have identified a performance bug
> > in RCU expedited grace periods.
> >
>
> I should add that we also tested the normal synchronize_rcu() on the
> same x86 machine, and the rcuperf figures were about 10 times slower
> than those of synchronize_rcu_expedited().
>
> Is this expected for synchronize_rcu()?

Yes, this is a deliberate design decision. The goal of
synchronize_rcu() is to minimize CPU overhead, which it does by
aggressively batching concurrent requests -- and also by batching
not-quite-so-concurrent requests. The other end of this tradeoff is that
synchronize_rcu() has relatively high latency. In contrast, the goal of
synchronize_rcu_expedited() is lower latency, with the penalty of higher
CPU utilization and more disturbance of real-time workloads. Note that
synchronize_prcu()'s use of IPIs disturbs real-time workloads in a manner
similar to synchronize_rcu_expedited(), but that synchronize_prcu()
further disturbs idle CPUs. In my experience, disturbing idle CPUs
doesn't make the people with battery-powered systems very happy.

Thanx, Paul

> Best,
> Lihao.
>
> > Thanx, Paul
> >
> >> Many thanks,
> >> Lihao.
> >>
> >> > I have a few comments on some of your patches based on a quick scan
> >> > through them.
> >> >
> >> > Thanx, Paul
> >> >
> >> >> Best wishes,
> >> >> Lihao.
> >> >>
> >> >>
> >> >> Lihao Liang (15):
> >> >> rcutorture: Add PRCU rcu_torture_ops
> >> >> rcutorture: Add PRCU test config files
> >> >> rcuperf: Add PRCU rcu_perf_ops
> >> >> rcuperf: Add PRCU test config files
> >> >> rcuperf: Set gp_exp to true for tests to run
> >> >> prcu: Implement call_prcu() API
> >> >> prcu: Implement PRCU callback processing
> >> >> prcu: Implement prcu_barrier() API
> >> >> rcutorture: Test call_prcu() and prcu_barrier()
> >> >> rcutorture: Add basic ARM64 support to run scripts
> >> >> prcu: Add PRCU Kconfig parameter
> >> >> prcu: Comment source code
> >> >> rcuperf: Add config files with various CONFIG_NR_CPUS
> >> >> rcutorture: Add scripts to run experiments
> >> >> Add GPLv2 license
> >> >>
> >> >> Heng Zhang (1):
> >> >> prcu: Add PRCU implementation
> >> >>
> >> >> include/linux/interrupt.h | 3 +
> >> >> include/linux/prcu.h | 122 +++++
> >> >> include/linux/rcupdate.h | 1 +
> >> >> init/Kconfig | 7 +
> >> >> init/main.c | 2 +
> >> >> kernel/rcu/Makefile | 1 +
> >> >> kernel/rcu/prcu.c | 497 +++++++++++++++++++++
> >> >> kernel/rcu/rcuperf.c | 33 +-
> >> >> kernel/rcu/rcutorture.c | 40 +-
> >> >> kernel/rcu/tree.c | 1 +
> >> >> kernel/sched/core.c | 2 +
> >> >> kernel/time/timer.c | 2 +
> >> >> kvm.sh | 452 +++++++++++++++++++
> >> >> run-rcuperf.sh | 26 ++
> >> >> .../testing/selftests/rcutorture/bin/functions.sh | 17 +-
> >> >> .../selftests/rcutorture/configs/rcu/CFLIST | 5 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU02 | 27 ++
> >> >> .../selftests/rcutorture/configs/rcu/PRCU02.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU03 | 23 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU03.boot | 2 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU06 | 26 ++
> >> >> .../selftests/rcutorture/configs/rcu/PRCU06.boot | 5 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU07 | 25 ++
> >> >> .../selftests/rcutorture/configs/rcu/PRCU07.boot | 2 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU09 | 19 +
> >> >> .../selftests/rcutorture/configs/rcu/PRCU09.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/CFLIST | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU | 20 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-12 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-12.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-14 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-14.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-15 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-15.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-16 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-16.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-2 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-2.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-32 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-32.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-4 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-4.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-48 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-48.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-56 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-56.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-60 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-60.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-62 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-62.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-64 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-64.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU-8 | 21 +
> >> >> .../rcutorture/configs/rcuperf/PRCU-8.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/PRCU.boot | 1 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-12 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-14 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-15 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-16 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-2 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-32 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-4 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-48 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-56 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-60 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-62 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-64 | 21 +
> >> >> .../selftests/rcutorture/configs/rcuperf/TREE-8 | 21 +
> >> >> 68 files changed, 1918 insertions(+), 5 deletions(-)
> >> >> create mode 100644 include/linux/prcu.h
> >> >> create mode 100644 kernel/rcu/prcu.c
> >> >> create mode 100755 kvm.sh
> >> >> create mode 100755 run-rcuperf.sh
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU02
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU02.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU03
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU03.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU06
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU06.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU07
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU07.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU09
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU09.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-12
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-12.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-14
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-14.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-15
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-15.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-16
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-16.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-2
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-2.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-32
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-32.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-4
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-4.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-48
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-48.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-56
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-56.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-60
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-60.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-62
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-62.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-64
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-64.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-8
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-8.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU.boot
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-12
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-14
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-15
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-16
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-2
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-32
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-4
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-48
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-56
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-60
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-62
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-64
> >> >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-8
> >> >>
> >> >> --
> >> >> 2.14.1.729.g59c0ea183
> >> >>
> >> >
> >>
> >
>