[Monotone-devel] read and select (was: Performance improvement splitout)

[Daniel Carosone]

On Mon, Sep 04, 2006 at 05:42:45PM -0700, Eric Anderson wrote:
> Oddly making this change significantly increases the amount of user
> time; haven't investigated why as the tradeoff for reduced wall clock
> time is a win.  Best guess is that because the client is running
> faster, it makes more recv calls for less data.

Likely, and the likely wall clock side of the tradeoff comes from
those reads sending window updates to the remote side that will allow
it to send more data sooner and keep tcp streaming.  Watching a pull
with tcptrace shows some pretty bursty behaviour and windows closing
right down for long periods.

If we're waiting for disk here, ok, but anything we can do to overlap
disk and network waits by getting the sender going at the same time is
a win, that's likely what's happening here.  On the localhost sync,
the RTT latencies are much less significant, even if they are
serialised with disk latencies.

--
Dan.

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