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

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Message-ID: <51CD1FEA.5020603@linux.intel.com>
Date:	Fri, 28 Jun 2013 08:32:26 +0300
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <erdnetdev@...il.com>,
	Ben Hutchings <bhutchings@...arflare.com>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Or Gerlitz <or.gerlitz@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Alex Rosenbaum <alexr@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v4 net-next] net: poll/select low latency socket support

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
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