linux-kernel - Re: [tip:core/rcu] rcutorture: Make initrd/init execute in userspace

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Message-ID: <20181204222412.GA6874@localhost>
Date:   Tue, 4 Dec 2018 14:24:13 -0800
From:   Josh Triplett <josh@...htriplett.org>
To:     tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
        paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/rcu] rcutorture: Make initrd/init execute in userspace

On Tue, Dec 04, 2018 at 02:09:42PM -0800, tip-bot for Paul E. McKenney wrote:
> --- a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
> +++ b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh
> @@ -39,9 +39,22 @@ mkdir $T
>  
>  cat > $T/init << '__EOF___'
>  #!/bin/sh
> +# Run in userspace a few milliseconds every second.  This helps to
> +# exercise the NO_HZ_FULL portions of RCU.
>  while :
>  do
> -	sleep 1000000
> +	q=
> +	for i in \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \
> +		a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a

Ow. If there's no better way to do this, please do at least comment how many 'a's
this is. (And why 186, exactly?)

Please also consider calibrating the delay loop as you do in the C code.