linux-kernel - Re: [ANNOUNCE] v5.9.1-rt19

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Message-ID: <20201027103411.h5ushvwsrovxls5u@beryllium.lan>
Date:   Tue, 27 Oct 2020 11:34:11 +0100
From:   Daniel Wagner <wagi@...om.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Clark Williams <williams@...hat.com>
Subject: Re: [ANNOUNCE] v5.9.1-rt19

On Tue, Oct 27, 2020 at 11:28:51AM +0100, Sebastian Andrzej Siewior wrote:
> Is it running as a RT task?

root@c2d:~/rt-tests# ./pi_stress
Starting PI Stress Test
Number of thread groups: 1
Duration of test run: infinite
Number of inversions per group: unlimited
     Admin thread SCHED_FIFO priority 4
1 groups of 3 threads will be created
      High thread SCHED_FIFO priority 3
       Med thread SCHED_FIFO priority 2
       Low thread SCHED_FIFO priority 1

It says so, let me double check if those task really run with SCHED_FIFO.

> Do you have RCU-boosting enabled?

Yes

#
# RCU Subsystem
#
CONFIG_TREE_RCU=y
CONFIG_PREEMPT_RCU=y
CONFIG_RCU_EXPERT=y
CONFIG_SRCU=y
CONFIG_TREE_SRCU=y
CONFIG_TASKS_RCU_GENERIC=y
CONFIG_TASKS_RCU=y
CONFIG_TASKS_RUDE_RCU=y
CONFIG_RCU_STALL_COMMON=y
CONFIG_RCU_NEED_SEGCBLIST=y
CONFIG_RCU_FANOUT=64
CONFIG_RCU_FANOUT_LEAF=16
CONFIG_RCU_BOOST=y
CONFIG_RCU_BOOST_DELAY=500
CONFIG_RCU_NOCB_CPU=y
# CONFIG_TASKS_TRACE_RCU_READ_MB is not set
# end of RCU Subsystem

> Otherwise it looks that if you throw enough non-RT load on the system,
> RCU can not catch up which does not sound good.

I think this is what Clark tried to tell me. If I understood him
correctly the test tool is not correct though.