Date: Mon, 11 Dec 2017 08:32:43 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: lianglihao@huawei.com
Cc: guohanjun@huawei.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, lihao.liang@gmail.com
Subject: Re: [PATCH] rcutorture: Add basic ARM64 support to run scripts
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On Fri, Dec 08, 2017 at 06:13:43PM +0800, lianglihao@huawei.com wrote:
> From: Lihao Liang <lianglihao@huawei.com>
> 
> This commit adds support of the qemu command qemu-system-aarch64
> to rcutorture. Use the following command to run:
> 
>   ./kvm.sh --qemu-cmd qemu-system-aarch64
> 
> Signed-off-by: Lihao Liang <lianglihao@huawei.com>

Nice!!!  Getting ARM support for rcutorture has been on my todo list
for some time!

A few questions and comments below.

Feedback from ARM experts also welcome!

							Thanx, Paul

> ---
> 
> The max CPUs supported by qemu machine 'virt' is 8 so the value of
> CONFIG_NR_CPUS in some test configuration files needs to be adjusted.
> 
>  tools/testing/selftests/rcutorture/bin/functions.sh | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/rcutorture/bin/functions.sh b/tools/testing/selftests/rcutorture/bin/functions.sh
> index 07a1377..5ffe4fe 100644
> --- a/tools/testing/selftests/rcutorture/bin/functions.sh
> +++ b/tools/testing/selftests/rcutorture/bin/functions.sh
> @@ -136,6 +136,9 @@ identify_boot_image () {
>  		qemu-system-x86_64|qemu-system-i386)
>  			echo arch/x86/boot/bzImage
>  			;;
> +		qemu-system-aarch64)
> +			echo arch/arm64/boot/Image
> +			;;
>  		*)
>  			echo vmlinux
>  			;;

Is it possible to automatically select ARM based on the kernel binary?
See the identify_qemu function for how this is done for i386, x86_64,
and PowerPC.  Can an "elif" be added for ARM?

> @@ -185,7 +188,14 @@ identify_qemu_append () {
>  	then
>  		echo root=/dev/sda
>  	else
> -		echo console=ttyS0
> +		case "$1" in
> +		qemu-system-aarch64)
> +			echo console=ttyAMA0
> +			;;
> +		*)
> +			echo console=ttyS0
> +			;;
> +		esac
>  	fi
>  }

This approach is going to result in very ugly nesting if support is
added for additional CPU families.  How about something like this?

identify_qemu_append () {
	local console=ttyS0

	case "$1" in
	qemu-system-x86_64|qemu-system-i386)
		echo noapic selinux=0 initcall_debug debug
		;;
	qemu-system-aarch64)
		console=ttyAMA0
		;;
	esac
	if test -n "$TORTURE_QEMU_INTERACTIVE"
	then
		echo root=/dev/sda
	else
		echo console=$console
	fi
}

> @@ -197,6 +207,9 @@ identify_qemu_args () {
>  	case "$1" in
>  	qemu-system-x86_64|qemu-system-i386)
>  		;;
> +	qemu-system-aarch64)
> +		echo -M virt -cpu host
> +		;;
>  	qemu-system-ppc64)
>  		echo -enable-kvm -M pseries -nodefaults
>  		echo -device spapr-vscsi
> @@ -257,6 +270,9 @@ specify_qemu_cpus () {
>  		qemu-system-x86_64|qemu-system-i386)

How about the following instead, eliminating the need for an additional
case?

 		qemu-system-x86_64|qemu-system-i386!qemu-system-aarch64)

>  			echo $2 -smp $3
>  			;;
> +		qemu-system-aarch64)
> +			echo $2 -smp $3
> +			;;
>  		qemu-system-ppc64)
>  			nt="`lscpu | grep '^NUMA node0' | sed -e 's/^[^,]*,\([0-9]*\),.*$/\1/'`"
>  			echo $2 -smp cores=`expr \( $3 + $nt - 1 \) / $nt`,threads=$nt
> -- 
> 2.7.4
>