AMD Prepares Zen 4 IBS ‘Instruction-Based Sampling’ Extensions for Linux


AMD recently submitted the company’s instruction-based sampling (IBS) capabilities for use in Linux performance subsystem and utility. This new submission from the company is the first official patch for the Zen 4 series of processors.

Instruction-based sampling support for upcoming AMD Zen 4 CPUs on Linux

Previous and current patch sets for the new AMD Zen 4 family had basic and lackluster terminology. With the latest patches being reviewed, users can rest assured that support for Zen 4 Linux is currently taking effect and will be seen in all new open source OS patches and updates.

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Zen 4 is set to improve instruction-based sampling by creating an additional data source extension and a new L3 cache error filtering capability.

Zen 4 IBS new features commented priority changes:

The DataSrc extension provides additional data source details for tagged load/store operations. Added support for these new bits in the script performance/raw dump report.

IBS L3 failure filtering works by tagging an instruction on IBS counter overflow and generating an NMI if the tagged instruction causes an L3 failure. Samples without L3 failure are discarded and the counter is reset with a random value (between 1-15 for recover pmu and 1-127 for op pmu). This helps reduce sampling overhead when the user is only interested in these samples. One of the use cases for these filtered samples is to provide data to the page migration daemon in multilevel memory systems.

Added support for L3 missing filtering in IBS driver via new pmu attribute “l3missonly”.

Linux users will be able to read the mailing list on the official Linux kernel site regarding new information about the Zen 4 IBS patch.

In summary, apart from sampling based on performance instructions, the new submission for selection is also beneficial for a gradually increasing number of features to be compiled to provide the ability to return hardware sampling results from performance to the compiler to aid profile-based design. and optimized binaries. Intel has been more aggressive with features and hardware performance counters being developed under the upcoming Linux operating system. Besides seeing the use for profiling possible optimization and issues that will require debugging, AMD enabling their IBS Zen 4 capability is great for the business.

Source: Phoronix


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