Re: [PATCH v9 net-next 5/7] net: simple poll/select low latency socketpoll

From: Eliezer Tamir
Date: Wed Jun 05 2013 - 09:41:59 EST

On 05/06/2013 16:30, Eric Dumazet wrote:
On Wed, 2013-06-05 at 13:34 +0300, Eliezer Tamir wrote:
A very naive select/poll busy-poll support.
Add busy-polling to sock_poll().
When poll/select have nothing to report, call the low-level
sock_poll() again until we are out of time or we find something.
Right now we poll every socket once, this is suboptimal
but improves latency when the number of sockets polled is not large.

Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
Tested-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: Eliezer Tamir <eliezer.tamir@xxxxxxxxxxxxxxx>

I am a bit uneasy with this one, because an applicatio polling() on one
thousand file descriptors using select()/poll(), will call sk_poll_ll()
one thousand times.

But we call sk_poll_ll() with nonblock set, so it will only test once
for each socket and not loop.

I think this is not as bad as it sounds.
We still honor the time limit on how long to poll.

When we busy-wait on a single socket we call sk_poll_ll() repeatedly
until we timeout or we have something to report.

Here on the other hand, we sk_poll_ll() once for each file, so we loop on the files. We moved the loop from inside sk_poll_ll to select/poll.

I also plan on improving this this in the next stage.

The plan is to give control on whether sk_poll_ll is called to
select/poll/epoll, so the caller has even more control.


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