Benchmarks.md

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.17134.706 (1803/April2018Update/Redstone4)
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
Frequency=2531252 Hz, Resolution=395.0614 ns, Timer=TSC
  [Host]     : .NET Framework 4.7.2 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3394.0
  DefaultJob : .NET Framework 4.7.2 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3394.0

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
LogFilter	2.443 us	0.0127 us	0.0118 us	0.2098	-	-	1008 B

Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using log4net;
using log4net.Appender;
using log4net.Config;
using log4net.Core;
using log4net.Filter;
using log4net.Layout;
using log4net.Repository.Hierarchy;
using System;

namespace ConsoleApp4
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Tests>();
        }
    }

    [MemoryDiagnoser]
    public class Tests
    {
        static readonly ILog _log = CreateLog();
        static ILog CreateLog()
        {
            var layout = new PatternLayout("%utcdate %-5level - %message%newline");
            layout.ActivateOptions();
            var appender = new FileAppender
            {
                Layout = layout,
                File = "C:/tmp/test.log",
            };
            appender.AddFilter(new LevelRangeFilter
            {
                LevelMax = Level.Fatal,
                LevelMin = Level.Info
            });
            appender.ActivateOptions();
            BasicConfigurator.Configure(appender);

            var log = LogManager.GetLogger(typeof(Tests));
            ((Logger)log.Logger).AddAppender(appender);

            return log;
        }

        [Benchmark]
        public void LogFilter()
        {
            _log.Debug("1");
            _log.Debug("2");
            _log.Debug("3");
            _log.Debug("4");
            _log.Debug("5");
            _log.Debug("6");
        }
    }
}