If you are a new customer, register now for access to product evaluations and purchasing capabilities. Need access to an account? If your company has an existing Red Hat account, your organization administrator can. Useful kernel and driver performance tweaks for your Linux server at time to bleed by Joe Damato. This article is going to address some kernel and driver tweaks that are interesting and useful. We use several of these in production with excellent performance, but you should proceed with caution and do research prior to trying anything listed below. Tickless System. The tickless kernel feature allows for on- demand timer interrupts. This means that during idle periods, fewer timer interrupts will fire, which should lead to power savings, cooler running systems, and fewer useless context switches. Kernel option: CONFIG. When a timer interrupt fires on a CPU, the process running on that CPU is interrupted while the timer interrupt is handled. Reducing the rate at which the timer fires allows for fewer interruptions of your running processes. This is extremely useful for process monitoring. You can build a simple system (or use an existing one like god) to watch mission- critical processes. If the processes die due to a signal (like SIGSEGV, or SIGBUS) or exit unexpectedly you’ll get an asynchronous notification from the kernel. The processes can then be restarted by your monitor keeping downtime to a minimum when unexpected events occur. Kernel options: CONFIG. This feature allows the kernel to offload the work of dividing large packets into smaller packets to the NIC. This article is going to address some kernel and driver tweaks that are interesting and useful. We use several of these in production with excellent performance, but you should proceed with caution and do research prior to. Nessus Plugins Fedora Local Security Checks. Fedora 23 : libksba (2016-db62a2d5a6) Fedora 23 : mediawiki (2016-ce1678471e) Fedora 23 : 389-ds-base (2016-b1a36cccc8). Summary of the changes and new features merged in the Linux Kernel during the 2.6.32 development cycle.Summary of the changes and new features merged in the Linux kernel during the 4.6 development cycle. Disk Drives: format prtvtoc <device> cfgadm -al fcinfo hba-port luxadm probe mpathadm list initiator-port mpathadm show <initiator-port name> iscsiadm list initiator-node iscsiadm list discovery format -e (to convert EFI. Note For the latest version of this manual associated with this Yocto Project release, see the Yocto Project Mega-Manual from the Yocto Project website. This frees up the CPU to do more useful work and reduces the amount of overhead that the CPU passes along the bus. If your NIC supports this feature, you can enable it with ethtool. This option increases network throughput as the DMA engine allows the kernel to offload network data copying from the CPU to the DMA engine. This frees up the CPU to do more useful work. Check to see if it’s enabled. Check the directories under /sys/class/dma/. Kernel options: CONFIG. DCA allows a driver to warm a CPU cache. A few NICs support DCA, the most popular (to my knowledge) is the Intel 1. Gb. E driver (ixgbe). Refer to your NIC driver documentation to see if your NIC supports DCA. To enable DCA, a switch in the BIOS must be flipped. Some vendors supply machines that support DCA, but don’t expose a switch for DCA. If that is the case, see my last blog post for how to enable DCA manually. You can check if DCA is enabled. NAPI provides two major features. Interrupt mitigation: High- speed networking can create thousands of interrupts per second, all of which tell the system something it already knew: it has lots of packets to process. NAPI allows drivers to run with (some) interrupts disabled during times of high traffic, with a corresponding decrease in system load. Packet throttling: When the system is overwhelmed and must drop packets, it’s better if those packets are disposed of before much effort goes into processing them. NAPI- compliant drivers can often cause packets to be dropped in the network adaptor itself, before the kernel sees them at all. Many recent NIC drivers automatically support NAPI, so you don’t need to do anything. Some drivers need you to explicitly specify NAPI in the kernel config or on the command line when compiling the driver. If you are unsure, check your driver documentation. A good place to look for docs is in your kernel source under Documentation, available on the web here: http: //lxr. Documentation/networking/ but be sure to select the correct kernel version, first! Older e. 10. 00 drivers (newer drivers, do nothing): make CFLAGS. The e. 10. 00e driver allows you to pass a command line option Interrupt. Throttle. Rate when loading the module with insmod. For the e. 10. 00e there are two dynamic interrupt throttle mechanisms, specified on the command line as 1 (dynamic) and 3 (dynamic conservative). The adaptive algorithm traffic into different classes and adjusts the interrupt rate appropriately. The difference between dynamic and dynamic conservative is the the rate for the “Lowest Latency” traffic class, dynamic (1) has a much more aggressive interrupt rate for this traffic class. As always, check your driver documentation for more information. With modprobe: insmod e. Interrupt. Throttle. Rate=1. Process and IRQ affinity. Linux allows the user to specify which CPUs processes and interrupt handlers are bound. Processes You can use taskset to specify which CPUs a process can run on. Interrupt Handlers The interrupt map can be found in /proc/interrupts, and the affinity for each interrupt can be set in the file smp. Doing this ensures that the data loaded into the CPU cache by the interrupt handler can be used (without invalidation) by the process; extremely high cache locality is achieved. There is a kernel driver for oprofile which generates collects data in the x. See oprofile’s homepage for more information. Kernel options: CONFIG. The epoll interface is designed to easily scale to large numbers of file descriptors. Make sure to select the correct kernel version because docs change as the source changes! Thanks for reading and don’t forget to subscribe (via RSS or e- mail) and follow me on twitter.
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