netdev - Re: [PATCH v8 net-next 5/7] net: simple poll/select low latency socket poll

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Message-ID: <51ADAADD.4030209@linux.intel.com>
Date:	Tue, 04 Jun 2013 11:52:45 +0300
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.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>,
	Alex Rosenbaum <alexr@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v8 net-next 5/7] net: simple poll/select low latency socket
 poll

On 03/06/2013 16:59, Eliezer Tamir wrote:
> On 03/06/2013 16:15, Eric Dumazet wrote:
>> On Mon, 2013-06-03 at 11:02 +0300, Eliezer Tamir wrote:
>>>       sock = file->private_data;
>>> -    return sock->ops->poll(file, sock, wait);
>>> +
>>> +    poll_result = sock->ops->poll(file, sock, wait);
>>> +
>>> +    if (!(poll_result & (POLLRDNORM | POLLERR | POLLRDHUP |
>>> POLLHUP)) &&
>>> +        sk_valid_ll(sock->sk) && sk_poll_ll(sock->sk, 1))
>>> +            poll_result = sock->ops->poll(file, sock, NULL);
>>> +
>>> +    return poll_result;
>>>   }
>>>
>>>   static int sock_mmap(struct file *file, struct vm_area_struct *vma)
>>>
>>
>>
>> In fact, for TCP, POLLOUT event being ready can also be triggered by
>> incoming messages, as the ACK might allow the user application to push
>> more data in the write queue.
>>
>> And you might check wait->_key to avoid testing flags that user is not
>> interested into.
>
> yes, comparing to _key is more correct.
> In any case this needs to be completely rewritten for support for
> working well with a large number of sockets.
>

Is it possible for wait to be NULL? (do we need to check for that?)
I see that poll_does_not_wait() checks for that, but I could not find
anywhere this is actually done.

-Eliezer

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