Message-ID: <51C05FC1.4000201@linux.intel.com>
Date: Tue, 18 Jun 2013 16:25:21 +0300
From: Eliezer Tamir <eliezer.tamir@linux.intel.com>
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To: Eric Dumazet <eric.dumazet@gmail.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>,
        Alex Rosenbaum <alexr@mellanox.com>,
        Avner Ben Hanoch <avnerb@mellanox.com>, Or Kehati <ork@mellanox.com>,
        sockperf-dev@googlegroups.com, Eliezer Tamir <eliezer@tamir.org.il>
Subject: Re: [PATCH v2 net-next] net: poll/select low latency socket support
References: <20130618085759.10941.15811.stgit@ladj378.jer.intel.com>  <20130618085810.10941.55039.stgit@ladj378.jer.intel.com> <1371551139.3252.249.camel@edumazet-glaptop>
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On 18/06/2013 13:25, Eric Dumazet wrote:
> On Tue, 2013-06-18 at 11:58 +0300, Eliezer Tamir wrote:

>> @@ -731,7 +755,11 @@ static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
>>   			mask = DEFAULT_POLLMASK;
>>   			if (f.file->f_op && f.file->f_op->poll) {
>>   				pwait->_key = pollfd->events|POLLERR|POLLHUP;
>> +				if (try_ll)
>> +					pwait->_key |= POLL_LL;
>
> Well, why enforce POLL_LL ?
>
> Sure we do this for select() as the API doesn't allow us to add the LL
> flag, but poll() can do that.
>
> An application might set POLL_LL flag only on selected fds.

One other thing,
sock_poll() will only ll_poll if the flag was set _and_ the socket has a
none-zero value in sk->sk_ll_usec so you still only poll on sockets
that were enabled for LLS, not on every socket.

-Eliezer
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