Data structures

Windows Research Kernel @ HPI

Numbered Queued Spinlocks in the WRK

In a recent post, we covered the implementation of in-stack queued spinlocks, the recommended method to use queued spinlocks in drivers. In this article, we would like to extend the discussion to a second class of queued spinlocks: numbered queued spinlocks. These well-known locks use per processor, pre-allocated memory to store the processor's queue item. In this article, we will give a short overview over the existing queued spinlocks in the WRK, how they are initialized and how they are used.

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Queued Spinlocks in the WRK

A few days ago, we came up with a discussion on the advantages of queued spinlocks over normal spinlocks. The biggest advantage in our oppinion is that queued spinlocks guarantee a FIFO ordering among competing processors while normal spinlocks don't. In this article, we show the implementation of queued spinlocks in the WRK. We present the source code of the 64-bit version for two reasons: first, the 64-bit version contains the implementation in plain C and not in the Assembly language, and second, in the 32-bit version, queued spinlocks are implemented in the HAL, which is not available as source code. The rational behind the implementation remains however the same.

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NtCreateThread - memory allocations in kernel mode

In this post we try to determine how much kernel memory is required when creating a new thread. This amount of memory is relevant for the upper bound of the number of possible threads in the system as investigated in detail by Mark Russinovich.

For a starting point we looked at the system service call implementation of NtCreateThread and followed every possible code path down to memory allocation functions such as ExAllocatePoolWithTag.

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Lists are a basic data structure in any operating system kernel, e.g. used for thread queue management. The WRK provides a set of struct definitions and list related functions/macros. In this post a short survey of these elements is given.

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Measuring Spin-Locks

Inspired by work of Thomas Friebel on Lock-Holder Preemption we did some experiments with the Windows Research Kernel:

  • How can we measure the time a thread is spinning while waiting for a spin-lock?
  • Does lock-holder-preemption occur on Windows systems (using VMware Workstation)?

Unfortunately, we could not boot the WRK with Xen. Therefore, the results of our initial experiments which are described in this post can not be compared directly to the work done by Thomas Friebel in the Linux/Xen environment.

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Getting OS Information - The KUSER_SHARED_DATA Structure

Ever asked how Windows API retrieves the current time, the version of the OS, or whether an evaluation period has expired? This structure will answers some of these questions.

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