Re: [PATCH v10 net-next 0/6] net: low latency Ethernet devicepolling

From: Eric Dumazet
Date: Tue Jun 11 2013 - 03:32:56 EST

On Tue, 2013-06-11 at 09:49 +0300, Eliezer Tamir wrote:

> I would like to hear opinions on what needs to be added to make this
> feature complete.
> The list I have so far is:
> 1. add a socket option

Yes, please. I do not believe all sockets on the machine are candidate
for low latency. In fact very few of them should be, depending on the
number of cpu and/or RX queues.

> 2. support for poll/select

As long as the cost of llpoll is bounded per poll()/select() call it
will be ok.

> 3. support for epoll

For this one, I honestly do not know how to proceed.

epoll Edge Trigger model is driven by the wakeups events.

The wakeups come from frames being delivered by the NIC (for UDP/TCP

If epoll_wait() has to scan the list of epitem to be able to perform the
llpoll callback, it will be too slow : We come back to poll() model,
with O(N) execution time.

Ideally we would have to callback llpoll not from the tcp_poll(), but
right before putting current thread in wait mode.

> Also, would you accept a trailing whitespace cleanup patch for
> fs/select.c?

This has to be submitted to lkml

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