Quick Boot by Pete Dice

Author:Pete Dice
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2018-04-15T00:00:00+00:00

Early Initialization

The early phase of the BIOS/bootloader will do the minimum to get the memory and processor cores initialized.

In an UEFI-based system BIOS, the Security (SEC) and the pre-EFI initialization (PEI) phases are normally synonymous with “early initialization.” It doesn’t matter if legacy or UEFI BIOS is used; from a hardware point of view, the early initialization sequence is the same for a given system.

Single-Threaded Operation

In a multicore system, the bootstrap processor is the CPU core/thread that is chosen to boot the normally single-threaded system firmware. At RESET, all of the processors race for a semaphore flag bit in the chipset. The first finds it clear and in the process of reading it sets the flag; the other processors find the flag set and enter a WAIT for SIPI or halt state. The first processor initializes main memory and the application processors (APs) and continues with the rest of boot. A multiprocessor (MP) system does not truly enter MP operation until the OS takes over. While it is possible to do a limited amount of parallel processing during the UEFI boot phase, such as during memory initialization with multiple socket designs, any true multithreading activity would require changes to be made to the DXE phase of the UEFI solutions to allow for this. In order to have broad adoption, some obvious benefits would need to arise.

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