varnish bottleneck?

[Poul-Henning Kamp]

That is correct.

If you use "pipe", the TCP connection turns into a straight pipe
where bytes are moved from client to server, without further inspection,
until either side closes the TCP connection.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.