Running redis mode (on develop) causes high CPU usage

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The CPU graph for my set of workers:

The GC graph:

Something has changed between 1.12.3 and 2e3b9a0 that has caused this to skyrocket.

Otherwise, the homeserver seems to work in terms of federating and sending messages. It's just obsessed with GCing right now.

Memory usage has remained a bit low:

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CPU usage by requests:

[erikjohnston]

I suspect its due to the fact that it seems to be sending out about 1kHz of REMOTE_SERVER_UP commands from each process. Possibly there is a loop going on?

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Switching off Redis (but running the same commit) seemed to reduce CPU, and stop spamming REMOTE_SERVER_UP.

[erikjohnston]

I believe the cause of this is if the fact in current TCP mode if a worker detects a remote server has come back online it sends a REMOTE_SERVER_UP to master, which then proxies to other workers. When running with redis the master process still echoes the command back, which leads to an infinite loop as redis will echo it back to master again.

[Half-Shot]

I can confirm #7352 fixes the issue for me.