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Performance counter value may unexpectedly leap forward
Article ID: 274323 - View products that this article applies to.
This article was previously published under Q274323
The result that is returned by the QueryPerformanceCounter function may unexpectedly leap forward from time to time. This leap may represent several seconds.
This problem occurs as a result of a design defect in the peripheral component interconnect (PCI) to Industry Standard Architecture (ISA) bridge of some chipsets. This bridge is commonly referred to as the south bridge. The jump occurs under a heavy PCI bus load, when the operating system receives a series of unexpected results from the bridge. The operating system detects the unexpected results and computes an amount to add to the performance counter. This causes the returned result from QueryPerformanceCounter to jump forward.
Programs should watch for an unexpected jump by comparing the change in time as determined by successive calls to QueryPerformanceCounter with the change in time as determined by successive calls to the GetTickCount function. If there is a significant jump that is based on QueryPerformanceCounter(), but no similar increase that is based on GetTickCount, then it can be assumed that the performance counter just jumped forward. The code sample at the end of this article demonstrates how to do this.
This operating system's behavior is by design. The performance counter adjustment is necessary when the operating system obtains unreliable data from the chipset.
Design defects within a hardware chip are known as errata. These design defects may cause the product to deviate from published specifications. For information on errata in specific chipsets, please contact the hardware vendor for the chipset.
A machine's PCI components are identified by a PCI identifier within the following key in the Windows registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\PCIThe names of subkeys have the following form
VEN_xxxx&DEV_yyyy&SUBSYS_aaaaaaaa&REV_bbwhere xxxx:yyyy represents the PCI identifier.
Currently, chips with the following PCI identifiers are known to exhibit a jump in performance counter value:
This list will be updated as Microsoft observes the behavior in other chipsets.
Collapse this tableExpand this table
Sample CodeThe following sample code demonstrates the method described above for detecting performance counter leaps. If the code is run on a computer with the PIIX4 chipset, for example, this console application will sporadically report leaps in the performance counter value.
Article ID: 274323 - Last Review: November 21, 2006 - Revision: 3.1