Re: [PATCH] refperf: work around 64-bit division

From: Randy Dunlap <rdunlap@infradead.org>
To: Arnd Bergmann <arnd@arndb.de>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] refperf: work around 64-bit division
Date: Fri, 29 May 2020 15:12:51 -0700	[thread overview]
Message-ID: <9f86f377-9ef9-779f-2022-a2f5d35e7d37@infradead.org> (raw)
In-Reply-To: <20200529201600.493808-1-arnd@arndb.de>

On 5/29/20 1:15 PM, Arnd Bergmann wrote:
> A 64-bit division was introduced in refperf, breaking compilation
> on all 32-bit architectures:
> 
> kernel/rcu/refperf.o: in function `main_func':
> refperf.c:(.text+0x57c): undefined reference to `__aeabi_uldivmod'
> 
> Work it by using div_u64 to mark the expensive operation.
> 
> Fixes: bd5b16d6c88d ("refperf: Allow decimal nanoseconds")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested

Thanks.

> ---
>  kernel/rcu/refperf.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c
> index 47df72c492b3..c2366648981d 100644
> --- a/kernel/rcu/refperf.c
> +++ b/kernel/rcu/refperf.c
> @@ -386,7 +386,7 @@ static int main_func(void *arg)
>  		if (torture_must_stop())
>  			goto end;
>  
> -		result_avg[exp] = 1000 * process_durations(nreaders) / (nreaders * loops);
> +		result_avg[exp] = div_u64(1000 * process_durations(nreaders), nreaders * loops);
>  	}
>  
>  	// Print the average of all experiments
> @@ -397,9 +397,14 @@ static int main_func(void *arg)
>  	strcat(buf, "Threads\tTime(ns)\n");
>  
>  	for (exp = 0; exp < nruns; exp++) {
> +		u64 avg;
> +		u32 rem;
> +
>  		if (errexit)
>  			break;
> -		sprintf(buf1, "%d\t%llu.%03d\n", exp + 1, result_avg[exp] / 1000, (int)(result_avg[exp] % 1000));
> +
> +		avg = div_s64_rem(result_avg[exp], 1000, &rem);
> +		sprintf(buf1, "%d\t%llu.%03d\n", exp + 1, avg, rem);
>  		strcat(buf, buf1);
>  	}
>  
> 

-- 
~Randy