I was also looking at this code because it turns out to be a relatively high CPU consumer in a test:

CPU SAMPLES BEGIN (total = 4077726) Fri Aug 22 18:54:48 2014
rank self accum count trace method
1 59.97% 59.97% 2445241 301175 io.netty.channel.epoll.Native.epollWait
2 26.54% 86.51% 1082218 301216 io.netty.channel.epoll.Native.writevAddresses
3 4.85% 91.36% 197836 301205 java.net.SocketInputStream.socketRead0
4 1.91% 93.26% 77790 301261 io.netty.channel.epoll.Native.readAddress
5 0.49% 93.76% 20139 301591 java.lang.ThreadLocal$ThreadLocalMap.getEntryAfterMiss
6 0.16% 93.92% 6606 301660 ch.qos.logback.classic.LoggerContext.getTurboFilterChainDecision_0_3OrMore

This is a real-time ad bidder handling 20Kqps on a 8-core machine, so almost all CPU goes to low-level networking, partially thanks to JVM overheads with native I/O etc. So if I disregard the top 4 methods (93.26% accum), scaling the remaining application CPU usage (6.74% -> 100%), then the 0.16% absolute CPU used by getTurboFilterChainDecision_0_3OrMore() scales to ~2.4% of all CPU usage from the rest of my app; that seems to be a high overhead for logging decisions (app has lots of logging code, but always using isXxxEnabled() guards except when the log msg is a literal string).

I noticed that the Object[] params is never used by any of the TurboFilters. I guess the params are passed because it's an extension point, somebody may write their own TurboFilter which considers the params, but maybe this could be handled in a different way (e.g., with a marker interface that tells a filter needs to receive the params).

Another inefficiency is that when you have <3 params and the logging decision is ACCEPT, the wrapper Object[] will be created twice: for example, filterAndLog_1() will first invoke getTurboFilterChainDecision_1() which creates this Object[] for invoking getTurboFilterChainDecision(), and later getTurboFilterChainDecision_1() creates its own Object[] wrapper for calling buildLoggingEventAndAppend(). This may not be very important when the event is actually logged (an extra Object[] wrapper is very small overhead compared to the full logging work), but appenders can also decide to not log, in practice I expect this to be a common scenario in apps that configure most of their loggers "open" and use the appenders as an easy on/off switch for the whole firehose.