Jitter smoothingJitter smoothing
For the past several years, server-class customers have seen processor-based performance increase generation over generation. This
increase is due in a large part to increases in core counts and more efficient instruction set architectures. Unlike the preceding decades,
the base frequency of the CPU has stayed rather stable with performance improvements coming from increasing core counts and
architectural enhancements. However, processor vendors began to realize that not all workloads benefit from increased core counts, so
they introduced features that allow some cores to run opportunistically at higher frequencies if power headroom is available or other
cores are underutilized.
Although these opportunistic frequency upsides can increase performance, they also introduce an unwanted side effect. Frequency
shifting itself introduces computation jitter, or nondeterminism, and undesirable latency. Jitter and the latency associated with it create
problems for several customer segments. For example, high-frequency traders rely on time-sensitive transactions. They cannot tolerate
the microseconds of delay that can be added non-deterministically to a trade, caused by a frequency shift. These delays over time can
cost a trader upwards of millions of dollars. In other environments, servers running RTOS (real-time operating systems) to control
critical functionality cannot tolerate random latencies that happen when opportunistic-frequency features are left enabled.
The current trend for latency-sensitive customers is to disable the features that normally would result in increased application
performance because of the associated jitter. A trade executes faster if the processor runs faster, but if it comes at the cost of random
delay, the benefit of increased performance is lost.
Hewlett Packard Enterprise introduced the Processor Jitter Control feature in its Gen10 and later servers to enable customers to
achieve both frequency upside and low jitter. This feature is available for Gen10 and later servers using Intel Xeon Scalable Processors.
Servers using AMD processors do not support this feature. This feature allows the customer to remove or reduce jitter caused by
opportunistic frequency management, which results in better latency response and higher throughput performance.
Enabling the Processor Jitter Control feature might require changes to power management settings under the operating system.
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