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[bug#41720] [PATCH] store: Use buffered I/O for all protocol writes

From: Lars-Dominik Braun
Subject: [bug#41720] [PATCH] store: Use buffered I/O for all protocol writes
Date: Fri, 5 Jun 2020 11:11:51 +0200
User-agent: Mutt/1.10.1 (2018-07-13)


I did some digging to investigate why SSH-based guix operations are currently
so slow. One of the reasons seems to be that some operations write single words
to the socket and due to NOWAIT these result in a lot of small packets.

The attached patch modifies store.scm to buffer all writes, so that won’t happen
any more. I’m seeing about ~40% speedup (6.194s vs 10.075s for the best out of
five runs) for `GUIX_DAEMON_SOCKET=ssh://localhost guix environment guix --
true`, but it also seems to have a negative impact on UNIX domain socket
communication by ~10% (1.561s vs 1.385s). For the notorious r-learnr package
it’s still ~20% better (ssh, 16.620/21.418) and only ~3% worse (unix,
11.489/11.199). Keep in mind localhost has a much larger MTU and much lower
latency than usual networks though. It might benefit from having an even bigger
write buffer (64k vs. currently 8k).


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