Message-ID: <1370447966.24311.284.camel@edumazet-glaptop>
Subject: Re: [PATCH v9 net-next 2/7] net: add low latency socket poll
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Eliezer Tamir <eliezer.tamir@linux.intel.com>
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>,
        Ben Hutchings <bhutchings@solarflare.com>,
        Andi Kleen <andi@firstfloor.org>, HPA <hpa@zytor.com>,
        Eilon Greenstien <eilong@broadcom.com>,
        Or Gerlitz <or.gerlitz@gmail.com>, Amir Vadai <amirv@mellanox.com>,
        Eliezer Tamir <eliezer@tamir.org.il>
Date: Wed, 05 Jun 2013 08:59:26 -0700
In-Reply-To: <51AF5D5A.8030907@linux.intel.com>
References: <20130605103400.11172.49099.stgit@ladj378.jer.intel.com>
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	  <1370445714.24311.268.camel@edumazet-glaptop>
	  <51AF59B0.6080101@linux.intel.com>
	 <1370446760.24311.275.camel@edumazet-glaptop>
	 <51AF5D5A.8030907@linux.intel.com>
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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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