sure.
But the core problem remains: our loopback networking scalability is
poor. For plain localhost<->localhost connected sockets we hit the
loopback device lock for every packet, and this very much shows up on
real workloads on a quad already: the lock instruction in netif_rx is
the most expensive instruction in a sysbench DB workload.
and it's not just about scalability, the plain algorithmic overhead is
way too high as well:
$ taskset 1 ./bw_tcp -s
$ taskset 1 ./bw_tcp localhost
Socket bandwidth using localhost: 2607.09 MB/sec
$ taskset 1 ./bw_pipe
Pipe bandwidth: 3680.44 MB/sec
i dont think this is acceptable. Either we should fix loopback TCP
performance or we should transparently switch to VFS pipes as a
transport method when an app establishes a plain loopback connection (as
long as there are no frills like content-modifying component in the
delivery path of packets after a connection has been established - which
covers 99.9% of the real-life loopback cases).
I'm not suggesting we shouldnt use TCP for connection establishing - but
if the TCP loopback packet transport is too slow we should use the VFS
transport which is both more scalable, less cache-intense and has lower
straight overhead as well.
Ingo
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