linux-kernel - Re: [PATCH v9 net-next 2/7] net: add low latency socket poll

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Date:	Wed, 05 Jun 2013 08:59:26 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
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>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Or Gerlitz <or.gerlitz@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v9 net-next 2/7] net: add low latency socket poll

On Wed, 2013-06-05 at 18:46 +0300, Eliezer Tamir wrote:
> On 05/06/2013 18:39, Eric Dumazet wrote:
> > On Wed, 2013-06-05 at 18:30 +0300, Eliezer Tamir wrote:
> >> On 05/06/2013 18:21, Eric Dumazet wrote:
> 
> >>> It would also make sense to give end_time as a parameter, so that the
> >>> polling() code could really give  a end_time for the whole duration of
> >>> poll().
> >>>
> >>> (You then should test can_poll_ll(end_time) _before_ call to
> >>> ndo_ll_poll())
> >>
> >> how would you handle a nonblocking operation in that case?
> >> I guess if we have a socket option, then we don't need to handle none
> >> blocking any diffrent, since the user specified exactly how much time to
> >> waste polling. right?
> >
> > If the thread already spent 50us in the poll() system call, it for sure
> > should not call any ndo_ll_poll(). This makes no more sense at this
> > point.
> 
> what about a non-blocking read from a socket?
> Right now we assume this means poll only once since the application will 
> repeat as needed.
> 
> maybe add a "once" parameter that will cause sk_poll_ll() to ignore end 
> time and only try once?

extern bool __sk_poll_ll(struct sock *sk, cycles_t end);

static inline bool sk_poll_ll(struct sock *sk, bool nonblock)
{
	return __sk_poll_ll(sk, nonblock, ll_end_time());
}

In the poll() code, we should call ll_end_time() once, even if we poll
1000 fds.




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