> On Nov 9, 2022, at 11:18 AM, Zhenlei Huang <zlei.hu...@gmail.com> wrote: > > >> On Oct 22, 2022, at 6:14 PM, Hans Petter Selasky <h...@selasky.org >> <mailto:h...@selasky.org>> wrote: >> >> Hi, >> >> Some thoughts about this topic. > > Sorry for late response. > >> >> Delaying ACKs means loss of performance when using Gigabit TCP connections >> in data centers. There it is important to ACK the data as quick as possible, >> to avoid running out of TCP window space. Thinking about TCP connections at >> 30 GBit/s and above! > > In data centers, the bandwidth is much more and the latency is extremely low > (compared to WAN), sub-milliseconds . > The TCP window space is bandwidth multiply RTT. For a 30 GBit/s network it is > about 750KiB . I think that is trivial for a > datacenter server. > > 4.2.3.2 in RFC 1122 states: > > in a stream of full-sized segments there SHOULD be an ACK for at least > > every second segment > Even if the ACK every tenth segment, the impact of delayed ACKs on TCP window > is not significant ( at most > ten segments not ACKed in TCP send window ). > > Anyway, for datacenter usage the bandwidth is symmetric and the reverse path > ( TX path of receiver ) is sufficient. > Servers can even ACK every segment (no delaying ACK). > >> >> I think the implementation should be exactly like it is. >> >> There is a software LRO in FreeBSD to coalesce the ACKs before they hit the >> network stack, so there are no real problems there. > > I'm OK with the current implementation. > > I think upper layers (or application) have (business) information to indicate > whether delaying ACKs should be employed. > After googling I found there's a draft [1]. > > [1] Sender Control of Delayed Acknowledgments in TCP: > https://www.ietf.org/archive/id/draft-gomez-tcpm-delack-suppr-reqs-01.xml > <https://www.ietf.org/archive/id/draft-gomez-tcpm-delack-suppr-reqs-01.xml> Found the html / pdf / txt version of the draft RFC. https://datatracker.ietf.org/doc/draft-gomez-tcpm-ack-pull/
> >> >> --HPS >> >> > > Best regards, > Zhenlei
