Tom Jackson wrote:
I was looking at lighttpd performance
(at http://trac.lighttpd.net/trac/wiki/Docs%3APerformance )
Considering how well AOLserver stands up to lighttpd, my question was why does
lighttpd do better?
I was wondering if it had something to do with how aolserver does its
writes, in particular the Ns_ConnFlushDirect|Ns_ConnWrite -> Ns_ConnSend
-> NsConnSend -> DriverSend chain. Each connection thread writes to its
own socket and loops to ensure that all the data is written. It seems
at first glance that it would make more sense to hand the task of
writing to the connection back to the driver thread once the connection
thread is done with it, and the single driver thread could multiplex
sending over multiple sockets with a single poll loop as well as leaving
the connection threads free to do other work. This is the same as the
stated rationale for the Ns_QueueWait api - "I/O events are cheap so do
those upfront instead of having expensive connection threads burdened
with wasteful blocking I/O" but on the writing side instead of the
reading side.
Since this is such an obvious change, would I be correct in guessing
that it was either tried and discarded as an overall performance loss
(there would be alot of data being passed between threads meaning a lot
of copying or extra mutexes if the connection thread and the driver
thread both accessed the buffer concurrently), or rejected as an
incompatible api change (Ns_ConnSend would do something subtly
different, and I guess it could make it harder to detect an incompletely
sent result)?
-J
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