Subject: Re: [PATCH net-next 2/2] net: avoid calling sched_clock when LLS is off

From: Andi Kleen <[email-masked]>
Date: Fri, 28 Jun 2013 16:38:40 +0200

> diff --git a/fs/select.c b/fs/select.c
> index 79b876e..3654075 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -402,7 +402,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
>  	poll_table *wait;
>  	int retval, i, timed_out = 0;
>  	unsigned long slack = 0;
> -	unsigned int ll_flag = POLL_LL;
> +	unsigned int ll_flag = ll_get_flag();

Is that a global flag? That's still the wrong level. It should
look at something in the file descriptor (preferably without
fetching any new cache lines)

-Andi

>  
> +static inline unsigned int ll_get_flag(void)
> +{
> +	return sysctl_net_ll_poll ? POLL_LL : 0;
> +}