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From: Uladzislau Rezki <urezki@gmail.com>
Date: Mon, 11 Mar 2024 09:43:51 +0100
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>, RCU <rcu@vger.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@amd.com>,
	Boqun Feng <boqun.feng@gmail.com>, Hillf Danton <hdanton@sina.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
	Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH v6 0/6] Reduce synchronize_rcu() latency(v6)
Message-ID: <Ze7ER232fPpvGssC@pc636>
References: <20240308173409.335345-1-urezki@gmail.com>
 <63e54cb9-fd08-43c3-9f42-3627198634e8@paulmck-laptop>
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In-Reply-To: <63e54cb9-fd08-43c3-9f42-3627198634e8@paulmck-laptop>

On Fri, Mar 08, 2024 at 01:51:29PM -0800, Paul E. McKenney wrote:
> On Fri, Mar 08, 2024 at 06:34:03PM +0100, Uladzislau Rezki (Sony) wrote:
> > This is v6. It is based on the Paul's "dev" branch:
> > 
> > HEAD: f1bfe538c7970283040a7188a291aca9f18f0c42
> > 
> > please note, that patches should be applied from scratch,
> > i.e. the v5 has to be dropped from the "dev".
> > 
> > v5 -> v6:
> >  - Fix a race due to realising a wait-head from the gp-kthread;
> >  - Use our own private workqueue with WQ_MEM_RECLAIM to have
> >    at least one execution context.
> > 
> > v5: https://lore.kernel.org/lkml/20240220183115.74124-1-urezki@gmail.com/
> > v4: https://lore.kernel.org/lkml/ZZ2bi5iPwXLgjB-f@google.com/T/
> > v3: https://lore.kernel.org/lkml/cd45b0b5-f86b-43fb-a5f3-47d340cd4f9f@paulmck-laptop/T/
> > v2: https://lore.kernel.org/all/20231030131254.488186-1-urezki@gmail.com/T/
> > v1: https://lore.kernel.org/lkml/20231025140915.590390-1-urezki@gmail.com/T/
> 
> Queued in place of your earlier series, thank you!
> 
Thank you!

>
> Not urgent, but which rcutorture scenario should be pressed into service
> testing this?
> 
I tested with setting '5*TREE01 5*TREE02 5*TREE03 5*TREE04' apart of that
i used some private test cases. The rcutree.rcu_normal_wake_from_gp=1 has
to be passed also.

Also, "rcuscale" can be used to stress the "cur_ops->sync()" path:

<snip>
#! /usr/bin/env bash

LOOPS=1

for (( i=0; i<$LOOPS; i++ )); do
        tools/testing/selftests/rcutorture/bin/kvm.sh --memory 10G --torture rcuscale \
    --allcpus \
      --kconfig CONFIG_NR_CPUS=64 \
      --kconfig CONFIG_RCU_NOCB_CPU=y \
      --kconfig CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y \
      --kconfig CONFIG_RCU_LAZY=n \
      --bootargs "rcuscale.nwriters=200 rcuscale.nreaders=220 rcuscale.minruntime=50000 \
                         torture.disable_onoff_at_boot rcutree.rcu_normal_wake_from_gp=1" --trust-make
        echo "Done $i"
done
<snip>

--
Uladzislau Rezki