Here's the 4th follow-up post in my 10 Habits of Great Server Performance Tuners series. This one focuses on the fourth habit: Know Your BIOS.
My last blog talked about beginning your system tuning by consulting a block diagram. The other thing you should always look at is your system's BIOS. Many server BIOSes these days allow you to configure options that affect performance. Like everything in the performance world, which set of BIOS options will be best will depend on your workload!
First things first, how do you find this "BIOS"? Most servers have a menu called "Setup" (or something similar) that you can access while the system is booting, before it starts loading the operating system. This "Setup" menu allows you to access your system's BIOS. Changes that you make here will affect how the operating system can utilize your hardware, and in some cases how the hardware works. If you change something here, you usually have to reboot and then the change will "stick" through all future reboots (until you change it again). As platforms grow increasingly sophisticated, they are offering a widening array of user-configurable options in Setup. So a good practice is to examine all the menu options available whenever you get a new platform. Here are some of the most common options on Intel platforms that could affect performance:
Power Management - Intel's power management technology is designed to deliver lower power at idle and better performance/watt (without significantly lowering overall performance) in most circumstances. There are 2 types - P-States, which attempt to manage power while the processor is active, and C-States which work while the processor is idle. In some BIOSes, both of these features are combined into one option which you should enable. In other cases they are separated. If they are separate, here's what to look for:
Intel EIST (or "Enhanced Intel Speedstep" or "Intel Speedstep" or "GV3" on older platforms) - This is the P-State power management that works while the processor is active. Leave it enabled unless directed to change it by an Intel representative.
Intel C-States - If you have this option or something similar, it is referring to the power management used when the processor is idle. Enable all C-States unless directed by an Intel representative.
Hardware Prefetch or Adjacent Sector Prefetch - These options try to lower overall latencies in your platform by bringing data into the caches from memory before it is needed (so the application does not have to wait for the data to be read). In many situations the prefetchers increase performance, but there are some cases where they may not. If you don't have time to test these options, then go with the default. Intel tests the prefetch options on a variety of server workloads with each new processor and makes a recommendation to our platform partners on how they should be set. If, however, you are tuning and you have the time to experiment, try measuring performance using each of the prefetch setting combinations.
There are several other options that might affect performance on specific platforms. Some examples might be a snoop filter enable/disable switch, a setting to emphasize either bandwidth or latency for memory transactions, or a setting to enable or disable multi-threading. In these cases, if you don't have time to test, use your Intel or OEM representative's suggestion or go with the default setting.
Being familiar with how your system's BIOS is configured is another basic component of system tuning.
Keep watching The Server Room for information on the other 6 habits in the coming weeks.