Messages in this thread |  | | Date | Sat, 27 Jan 2018 15:41:54 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC 00/16] A new RCU implementation based on a fast consensus protocol |
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On Fri, Jan 26, 2018 at 11:57:44PM -0800, Paul E. McKenney 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@linux.vnet.ibm.com> wrote: > > > On Tue, Jan 23, 2018 at 03:59:25PM +0800, lianglihao@huawei.com wrote: > > >> From: Lihao Liang <lianglihao@huawei.com> > > >> > > >> 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.
And my guess is that the "rtbe: 1" is happening because you aren't doing anything with CPU hotplug. The way this could happen is as follows:
1. rcutorture does call_prcu() with a test callback on CPU 5.
2. CPU 5 goes offline, but its callbacks stay there.
3. rcutorture does prcu_barrier(), which queues a callback on each sufficiently online CPU. No callback is enqueued on CPU 5.
4. The enqueued callbacks are all invoked, so prcu_barrier() returns.
5. rcutorture complains because the test callback stranded on CPU 5 never did get invoked.
A slightly different sequence of events could strand one of prcu_barrier()'s callbacks on an offline CPU, in which case prcu_barrier() would hang until that CPU came back online. There are probably other failure scenarios, but those two should do for now. ;-)
Thanx, Paul
> > > 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@2.4GHz, 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@2.4GHz, 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. > > 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 > > >> > > > > >
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