On 10/28/2011 03:31 PM, David Miller wrote:

From: Daniel Baluta<redacted>
Date: Sat, 29 Oct 2011 00:35:24 +0300

quoted

On Sat, Oct 29, 2011 at 12:19 AM, David Miller[off-list ref]  wrote:

quoted

From: Daniel Baluta<redacted>
Date: Sat, 29 Oct 2011 00:14:03 +0300

quoted

+static inline int tcp_delack_thresh(const struct sock *sk)
+{
+     return inet_csk(sk)->icsk_ack.rcv_mss * sysctl_tcp_delack_segs;
+}
+

Please turn this into a shift or something, you're adding a multiply
into a core code path.

Is there any generic API to do this? Default case is not
affected since tcp_delack_segs is 1.

I'm saying make the tunable a shift count instead of something to
multiply against.

That would be loads faster, but won't that have issues with granularity? 
  It will allow 1, 2, 4, 8, 16, 32, etc segments but none of the umpteen 
values in between.  FWIW, HP-UX defaults to 22 segments, which IIRC has 
its basis in how many "typical" segments could fit in a 32KB window.

If the mss and the delack segs are being converted into an octet count, 
and multiplication or successive addition etc are too expensive, how 
about using an octet count directly?

rick jones