Subject: Re: [PATCH v4 net-next] net: poll/select low latency socket support

From: Eliezer Tamir <[email-masked]>
Date: Fri, 28 Jun 2013 08:32:26 +0300

On 28/06/2013 07:43, Andi Kleen wrote:
>> @@ -400,6 +402,8 @@ 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;
>> +	u64 ll_time = ll_end_time();
>
> So you're adding a sched_clock to every select call, even if it has
> nothing to do with ll?
>
> That seems rather drastic. select can be performance critical.

would the following be acceptable?

	unsigned int ll_flag = ll_poll_enabled(); // returns POLL_LL if on
	u64 ll_time = ll_flag ? ll_end_time() : 0;

and at the other side
	
	if (ll_flag && can_poll_ll(ll_end_time))
		continue;

-Eliezer