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Date: Fri, 28 Jun 2013 08:32:26 +0300
From: Eliezer Tamir <eliezer.tamir@linux.intel.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Don Skidmore <donald.c.skidmore@intel.com>,
        e1000-devel@lists.sourceforge.net,
        Willem de Bruijn <willemb@google.com>,
        Eric Dumazet <erdnetdev@gmail.com>,
        Ben Hutchings <bhutchings@solarflare.com>, HPA <hpa@zytor.com>,
        Eilon Greenstien <eilong@broadcom.com>,
        Or Gerlitz <or.gerlitz@gmail.com>, Amir Vadai <amirv@mellanox.com>,
        Alex Rosenbaum <alexr@mellanox.com>,
        Eliezer Tamir <eliezer@tamir.org.il>
Subject: Re: [PATCH v4 net-next] net: poll/select low latency socket support
References: <20130624072751.26134.78163.stgit@ladj378.jer.intel.com> <20130624072803.26134.41593.stgit@ladj378.jer.intel.com> <20130628044305.GQ6123@two.firstfloor.org>
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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