Weird rumble scores
← Thread:Talk:BeepBoop/Weird rumble scores/reply (4)
I'm not recording any data at this time no.
GC overhead is one potential issue, but I would argue that if rumble clients are causing massive skipped turns due to GC overhead, then the rumble client is likely badly configured, with something like too many rumble clients running concurrently for the number of CPU cores.
Java runs GC taking advantage of an additional thread generally, and it's normal for GC overhead to be significant for many bots, to the degree where I would argue that a rumble client should always be allocated two unused CPU cores, one for the main thread and one for GC thread overhead.
Since rumble clients are uploading scores after a few battles, it’s really hard that every core is used already. Not to mention that modern CPUs are great at reordering instructions, making room for more threads. So that leaving 1 more core for idle is completely wasting time & money IMO.
Anyway if rumble clients are commonly experiencing GC overhead, it could be solved by forcing full GC to run before each round. And if you’re still producing too much garbage even between rounds, it’s totally fine to be punished by skipped turns.
Anyway, GC overhead is always fair. If you are dealing with GC and skipped turns worse than the opponents, you get worse score, it’s perfectly judged.
I'm curious why you think GC overhead is always fair. Since GC overhead happens outside of the main thread, it can punish all robots in the same battle with a high degree of randomness. Not only that, if you're running a bunch of rumble clients on a computer, and the overall CPU usage on the system for all cores reaches 100% due to a couple clients having more GC overhead, then it could affect all bots in all active battles on that system, even in the other rumble clients.
Being fair means no one is getting advantage over it. And the ability to withstand ocationally skipped turns is part of the competition.
Since no one can guarantee that robots are always running with sufficent resource, I’m always on the side that robot authors should assume low performance computers.
"no one is getting advantage over it" is certainly untrue. Consider the notion of a bot that uses very little CPU in the main thread but creates lots of GC overhead, in a battle versus a bot that uses most of the typical CPU allotment but doesn't create much GC overhead. If this is on a system where the GC thread can affect the time available to the main thread (i.e. don't have enough spare CPU for the GC thread), then the bot that uses very little CPU in the main thread but is creating lots of GC overhead will be advantaged by causing the GC overhead, since it would cause more skipped turns for the other bot but not so much itself. This is somewhat of an extreme example, but the point is that skipped turns caused by GC overhead are anything but fairly distributed.
You are right. Apart from creating many thrads that do a lot of work when it’s others turn, creating a lot of objects to increase GC overhead does affect others’ bots as well, making the result a little bit random.
But I doubt how much difference can GC overhead put. The most unreproducible scores I experienced are always coming from some rare exceptions, say 1/1000. And once happened, it causes some random pairing to be close to 0. If averaged with some normal score, it really looked like it’s decreasing with no reason.
But there’s always some reason, and mostly coming from specific bot instead of the clients, since not everyone is affected.
So my advice is that you output exceptions to file, and check if there are any. Skipped turns could also be counted. I was doing this in older bots as well, and concluded that GC overhead & skipped turns aren’t really the problem, but exceptions are.
For the specific case I mentioned of ags.Glacier 0.3.0 versus lxx.Emerald 0.6.5, when it was at 1 battle, I thought it was likely some rare exception as you say, but then a 2nd battle came in with about the same low score as the 1st battle, and yet I'm not able to reproduce a result anything like that in many many tests. This leads me to believe that there is most likely something significantly different about the environment those two battles were run in, as compared to my own environment.
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I think you are right. Clients should be allocated with one extra core for GC to be ran on background. Forcing full GC each round could also be added to rumble client.
And I think the extra core should be enforced by rumble clients
Anyway the optimal cpu ratio needs some experiments, but battles seems to run even faster when some cores are dedicated for GC.
And I’m not sure whether rumble clients shall be restarted after many battles. If there were some memory leaks in robocode, performance will drop overtime, resulting APS drop in newer bots.
It's not per-round so much as per-battle, but I will note that Robocode does make some System.gc calls at end of battle.
It's also the case for a very long time I've been in a habit of including System.gc() in the constructor of my bots, so that'd end up being per round.