Today is one of these wacky days where nothing works (problems with kvm-tool, problems with RAM backed block device driver and kvm interaction and so on. But today was also the day of another Round of Vladimir Makarov gcc-versus-llvm round (gcc mailing list). To summary the highlights: LLVM is not faster as GCC (this is a often repeated lie): If you need the same generated code quality and compilation speed as LLVM -O2/-O3 you should use GCC with -O If you want 10%-40% faster generated code, you should use GCC with -O2/-O3 and you need 20%-40% more time for compilation (150%-200% if you use GCC LTO) Vladimir believe that LLVM code performance is far away from GCC because it is sufficiently easy to get first percents of code improvement, it becomes much harder to get subsequent percents Vladimir used this year -Ofast -flto -fwhole-program instead of -O3 for GCC and -O3 -ffast-math for LLVM....

The last two days I programmed an system with n input channels and n output channels. The system multiplex the input packet to the actual output channel, depending on packet IP destination address (and do some packet mangling, but this does not matter here). But the output channel can block (the socket returns EAGAIN, e.g. if TCP peer close the window). Each received packet is enqueued in the input queue. If the output channel is blocked then the input queue is stalled, no new packet can be transmitted, although the packet is indent for another output queue - this is bad....

Some thoughts about recent activity here at TCPM and some other places. Since several years vendors and web companies try to address web performance problems by adjusting TCP. Congestion control, slow start (IW10), timeouts and the like are addressed like a function of time: IW10 seems adequate for 2011, IW15 for 2013, IW20 for 2016 and so on. Timeouts are adjusted to current “consumer” networks. But the actual network characteristic is hardly a function of date, it is a function of the effective link characteristic between two endpoints in a packet switched networks with no a priori bandwidth guarantee....

Today a fresh I-D was published, titled: “Host/Host Protocol for the ARPA Network” from Alexander McKenzie and Steve Crocker; covering Internet history. Great I-D: This document reproduces the Host/Host Protocol developed by the ARPA Network Working Group during 1969, 1970 and 1971. It describes a protocol used to manage communication between processes residing on independent Hosts. It addresses issues of multiplexing multiple streams of communication over a single hardware interface including addressing, flow control, connection establishment/disestablishment, and other signaling....

Today I spent quite some hours in spotting some packet drops at Gigabit line rate. Stress-testing the hardware at line-rate reveal a lot of noise and disagreements: it is difficult to determine _what_ really is the source of packet drops. Due to some netperf and perf analysis and some new tracepoints the eyes focus on PCI express bus. Quite a lot of analysis until that, first I interpreted the raw values as a CPU limitation....

Last time as I posted about TCP fairness aspects of TCP I don’t touched the topic in great detail. But TCP fairness and protocol fairness in general is a important requirement in the whole IP communication zoo. In this blog posting I will write some sentences about the fairness aspects of a network layer protocol and particular TCP. UDP and Datagram based Protocols To start with UDP - as a unreliable, unordered lightweight datagram based service - provides no fairness mechanisms at all....

Traveling back from Berlin to Munich. This time via City-Night-Train booked in a six-person wagon. Reading “der Freitag”, a Berlin weekly newspaper produced here in Berlin until midnight. One of Kitas professor suggest the paper. I took this extended weekend (from Thursday) to arrange our new home in Weissensee/Berlin. Paint the rooms white and the floor in a special mixed color. Next time I will establish the parquet (84m^2). After that all ground work is done and the furniture can be ebayed[TM]....

Between 15th and 25th of July I was at Majorca/Spain for one week of relaxing (including a little bit of climbing). A really nice spot!

Quit interesting Westmere-EP CPU: of cores | 6 | of threads | 12 | Bus speed | 2933 MHz QPI | System Bus|5.86 GT/s| Level 1 cache size | 6 x 32 KB icache, 6 x 32 KB dcache | Level 2 cache size | 6 x 256 KB | Level 3 cache size | 12 MB | Features | SSE4.2, Turbo Boost, AES New Instructions, Enhanced Intel SpeedStep Technology. … | Max Memory Bandwidth | 32 GB/s| Memory Types| DDR3-800/1066/1333| Lithography| 32 nm|...