linux-kernel - Re: [PATCH rcu 11/15] rcutorture: Add reader

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Message-ID: <d27da29c-7499-4f08-b582-a2bbb9b3c1c7@paulmck-laptop>
Date: Tue, 12 Nov 2024 11:27:33 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org, Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>, bpf@...r.kernel.org
Subject: Re: [PATCH rcu 11/15] rcutorture: Add reader_flavor parameter for
 SRCU readers

On Tue, Nov 12, 2024 at 10:12:40AM +0530, Neeraj Upadhyay wrote:
> On 10/15/2024 9:41 PM, Paul E. McKenney wrote:
> > This commit adds an rcutorture.reader_flavor parameter whose bits
> > correspond to reader flavors.  For example, SRCU's readers are 0x1 for
> > normal and 0x2 for NMI-safe.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Andrii Nakryiko <andrii@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> > Cc: <bpf@...r.kernel.org>
> > ---
> >  .../admin-guide/kernel-parameters.txt         |  8 +++++
> >  kernel/rcu/rcutorture.c                       | 30 ++++++++++++++-----
> >  2 files changed, 30 insertions(+), 8 deletions(-)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 1518343bbe223..52922727006fc 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -5426,6 +5426,14 @@
> >  			The delay, in seconds, between successive
> >  			read-then-exit testing episodes.
> >  
> > +	rcutorture.reader_flavor= [KNL]
> > +			A bit mask indicating which readers to use.
> > +			If there is more than one bit set, the readers
> > +			are entered from low-order bit up, and are
> > +			exited in the opposite order.  For SRCU, the
> > +			0x1 bit is normal readers and the 0x2 bit is
> > +			for NMI-safe readers.
> > +
> >  	rcutorture.shuffle_interval= [KNL]
> >  			Set task-shuffle interval (s).  Shuffling tasks
> >  			allows some CPUs to go into dyntick-idle mode
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index f96ab98f8182f..405decec33677 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -111,6 +111,7 @@ torture_param(int, nocbs_nthreads, 0, "Number of NOCB toggle threads, 0 to disab
> >  torture_param(int, nocbs_toggle, 1000, "Time between toggling nocb state (ms)");
> >  torture_param(int, read_exit_delay, 13, "Delay between read-then-exit episodes (s)");
> >  torture_param(int, read_exit_burst, 16, "# of read-then-exit bursts per episode, zero to disable");
> > +torture_param(int, reader_flavor, 0x1, "Reader flavors to use, one per bit.");
> >  torture_param(int, shuffle_interval, 3, "Number of seconds between shuffles");
> >  torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable.");
> >  torture_param(int, stall_cpu, 0, "Stall duration (s), zero to disable.");
> > @@ -644,10 +645,20 @@ static void srcu_get_gp_data(int *flags, unsigned long *gp_seq)
> >  
> >  static int srcu_torture_read_lock(void)
> >  {
> > -	if (cur_ops == &srcud_ops)
> > -		return srcu_read_lock_nmisafe(srcu_ctlp);
> > -	else
> > -		return srcu_read_lock(srcu_ctlp);
> > +	int idx;
> > +	int ret = 0;
> > +
> > +	if ((reader_flavor & 0x1) || !(reader_flavor & 0x7)) {
> 
> Minor: Maybe use macros in place of 0x1, 0x2, 0x7 as a cleanup later.

Hmmm...

I could move SRCU_READ_FLAVOR_* to include/linux/srcu.h and make
rcutorture use those.  Plus have a combined mask for the instances of 0x7.

Or is there a better way?

							Thanx, Paul

> - Neeraj
> 
> > +		idx = srcu_read_lock(srcu_ctlp);
> > +		WARN_ON_ONCE(idx & ~0x1);
> > +		ret += idx;
> > +	}
> > +	if (reader_flavor & 0x2) {
> > +		idx = srcu_read_lock_nmisafe(srcu_ctlp);
> > +		WARN_ON_ONCE(idx & ~0x1);
> > +		ret += idx << 1;
> > +	}
> > +	return ret;
> >  }
> >  
>