Re: [PATCH v7 net-next 2/5] net: implement support for low latency socket polling

On 30/05/2013 18:07, Amir Vadai wrote:

On 30/05/2013 14:41, Eliezer Tamir wrote:

quoted

diff --git a/fs/select.c b/fs/select.c

@@ -486,6 +488,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
  			break;
  		}

+		if (can_poll_ll(ll_time))
+			continue;

I don't see here discrimination between sockets that you want to poll
and other sockets.
So it means that select will busy poll every type of file descriptor
instead of going to sleep.
Should have a condition with something like sk_valid_ll()

As I said earlier, select and poll are far from complete.
We are working on this.
Right now when you turn this on, all sockets get the same treatment.
sk_valid_ll() can't work here, because we don't have a single socket to 
work with.

At the moment, I think the right way to solve this might be to add
new flags to poll.h So that select/poll can signal to sock_poll
that it wants to busy-wait and sock_poll can tell select/poll that
it has found a socket that can support it.

Remember that the information is dynamic so we can't know in advance
which sockets can busy-poll.

If anyone else has a suggestion I would really like to hear it.

quoted

+static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
+{
+}
+
+static inline bool can_poll_ll(unsigned long end_time)

should use here cycles_t too.

yes

quoted

+{
+	return false;
+}
+
+#endif /* CONFIG_NET_LL_RX_POLL */
+#endif /* _LINUX_NET_LL_POLL_H */

Also, something general about this patch. I think you should split out
to separate patches all the users of the feature, like you did for TCP.
I would suggest small patches for UDP, select and poll.

Splitting out the users of the features as you call it will only move 
out about 30 lines of patch, I think it will make reviewing harder since 
you will not be able to see the whole picture in one patch.
But if anyone else thinks this is a good idea, I will do it.

-Eliezer

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