• Linux,  Work

    Enabling jumbo frames on your network

    Jumbo frames are Ethernet frames with up to 9000 bytes of payload, in contrast to normal frames which have up to 1500 bytes per payload. They are useful on fast (Gigabit Ethernet and faster) networks, because they reduce the overhead. Not only will it result in a higher throughput, it will also reduce CPU usage. To use jumbo frames, you whole network needs to support it. That means that your switch needs to support jumbo frames (it might need to be enabled by hand), and also all connected hosts need to support jumbo frames. Jumbo frames should also only be used on reliable networks, as the higher payload will make…

  • Linux,  Work

    FS-CACHE for NFS clients

    FS-CACHE is a system which caches files from remote network mounts on the local disk. It is a very easy to set up facility to improve performance on NFS clients. I strongly recommend a recent kernel if you want to use FS-CACHE though. I tried this with the 4.9 based Debian Stretch kernel a year ago, and this resulted in a kernel oops from time to time, so I had to disable it again. I’m currently using it again with a 4.19 based kernel, and I did not encounter any stability issues up to now. First of all, you will need a dedicated file system where you will store the…

  • Linux,  Work

    Debian Stretch on AMD EPYC (ZEN) with an NVIDIA GPU for HPC

    Recently at work we bought a new Dell PowerEdge R7425 server for our HPC cluster. These are some of the specifications: 2 AMD EPYC 7351 16-Core Processors 128 GB RAM (16 DIMMs of 8 GB) Tesla V100 GPU Our FAI configuration automatically installed Debian stretch on it without any problem. All hardware was recognized and working. The installation of the basic operating system took less than 20 minutes. FAI also sets up Puppet on the machine. After booting the system, Puppet continues setting up the system: installing all needed software, setting up the Slurm daemon (part of the job scheduler), mounting the NFS4 shared directories, etc. Everything together, the system…

  • Linux,  Work

    Linux performance improvements

    Two years ago I wrote an article presenting some Linux performance improvements. These performance improvements are still valid, but it is time to talk about some new improvements available. As I am using Debian now, I will focus on that distribution, but you should be able to easily implement these things on other distributions too. Some of these improvements are best suited for desktop systems, other for server systems and some are useful for both.

  • Linux,  Work

    Improving Mediawiki performance

    Now that I am on the subject of improving performance, I configured some performance improvements for a Mediawiki installation here: Make sure you run the latest Mediawiki version. Mediawiki 1.16 introduced a new localisation caching system which is supposed to improve performance, so you definitely want this to get the best performance. Create a directory where Mediawiki can store the localisation cache (make sure it is writable by your web server). By preference store it on a tmpfs (at least if you are sure it will be big enough to store the cache), and configure it in LocalSettings.php: $wgCacheDirectory = "/tmp/mediawiki"; Iif /tmp is on a tmpfs, you might add…

  • Linux,  Work

    Improving performance by using tmpfs

    Today I analyzed disk reads and writes on a server with iotop and strace and found some interesting possible optimizations. With iotop you can check which processes are reading and writing from the disks. I always press the o, p and a keys in iotop so that it only shows me processes doing I/O and so that it will show accumulated I/O instead of the bandwidth. With the left and right arrows I select on which columns to sort the list. Once you have identified the processes wich are doing much I/O, you can check what they are reading or writing with strace, for example # strace  -f -p $PID …

  • Linux,  Mandriva

    Speeding up my Linux system

    My Mandriva 2009.1 system at home had become a bit slow lately, and so I decided to do some attempts to make it a bit faster again. This is not the most powerful system anymore (Asus A8N-SlI NForce4 motherboard, Athlon 64 3500+, 3 GB RAM, 250 GB SATA-1 disk, NVidia 6600 GT graphics card), but it sometimes felt very slow because of lots of disk activity, especially during start-up. I succeeded in improving the performance noticeably: the disk activity now stops much earlier after log-in and after starting Evolution. I did some different changes at once and have not always measured what was the impact of each individual change. So…

  • Linux,  Uncategorized

    Fix bad performance with NVidia 177.80 drivers

    Since I upgraded to Nvidia’s beta driver series which were supposed to improve performance for KDE 4 (including the now stable version 177.80), my GNOME desktop on my system with a Geforce 6600 GT graphics card, felt a lot slower. It was most noticeable when browsing the web with Firefox. When quickly scrolling a web page with my mouse’s scroll wheel, X started eating 100% of CPU time and the image on the screen started lagging behind a lot. Also just rendering a page seemed to be much slower. Disabling smooth scrolling in Firefox, did not help at all. Searching on the web, I found out that I’m not the…