use TCP_NODELAY on TCP sockets?

[Erin Shepherd]

It seems absent from the BSDs, but on Linux you can pass the MSG_MORE flag to send() to override TCP_NODELAY for a specific write

On Wed, 15 May 2024, at 19:40, Job Snijders via Bird-users wrote:
> Dear Marco,
> 
> On Wed, 15 May 2024 at 19:27, Marco d'Itri <md at linux.it> wrote:
>> On May 15, Job Snijders via Bird-users <bird-users at network.cz> wrote:
>> 
>> > But please be very careful in considering this patch, because it does
>> > introduce some subtle changes in the on-the-wire behaviour of BIRD. For
>> > example, without this patch an UPDATE for a handful of routes and the
>> > End-of-RIB marker might end up in the same TCP packet (if this fits);
>> > but with this patch, the End-of-RIB marker ends up in its own TCP
>> > packet. As things are today, setting TCP_NODELAY will increase the
> 
>> 
>> I think that this can be fixed easily with TCP_CORK.
>> Basically, with TCP_NODELAY + TCP_CORK you can have the optimal balance 
>> of latency and overhead without using writev.
> 
> 
> Yes, thanks for sharing this suggestion.
> 
> Note that TCP_CORK is a Linux-only feature (on FreeBSD it seems aliased to TCP_NOPUSH, but I might be misunderstanding that code). There are subtle differences between NOPUSH and CORK: resetting CORK triggers a flush, whereas resetting NOPUSH does not.
> 
> It is of course reasonable to optimize one platform and not others, we work with the tools that we have - but a portable approach (using writev()?) would seem attractive to me :-)
> 
> Kind regards,
> 
> Job
>> 
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