How does Linux perf calculate the cache references and cache misses events?

How does Linux perf calculate the cache references and cache misses events?

perf uses the Performance Monitoring Units (PMUs) hardware in modern processors to collect data on hardware events such as cache accesses and cache misses without undue overhead on the system. The output also estimates the instructions per processor clock cycle (IPC).

How is cache miss rate calculated?

6 MEASURING CACHE EFFICIENCY. The miss rate is similar in form: the total cache misses divided by the total number of memory requests expressed as a percentage over a time interval. Note that the miss rate also equals 100 minus the hit rate.

How does perf work in Linux?

Perf is a facility comprised of kernel infrastructure for gathering various events and userspace tool to get gathered data from the kernel and analyze it. It is like a gprof, but it is non-invasive, low-overhead and profile the whole stack, including your app, libraries, system calls AND kernel with CPU!

What are cache references?

Processor reference that are found in the cache are called cache hits. References not found in the cache are called cache misses. On a cache miss, the cache control mechanism must fetch the missing data from memory and place it in the cache. Usually the cache fetches a spatial locality called the line from memory.

What are cache misses?

A cache miss is an event in which a system or application makes a request to retrieve data from a cache, but that specific data is not currently in cache memory. If the data is found in the main database, the data is then typically copied into the cache in anticipation of another near-future request for that same data.

How do you evaluate cache performance?

Another useful metric to test the performance is Power law of cache misses. It gives you the number of misses when you change the size of the cache, given that the number of misses for one of the cache sizes is known.

What happens when a cache miss occurs?

When a cache miss occurs, the system or application proceeds to locate the data in the underlying data store, which increases the duration of the request. Typically, the system may write the data to the cache, again increasing the latency, though that latency is offset by the cache hits on other data.

What is perf coding?

perf is a very powerful userspace command for tracing or counting both hardware and software events. Software events are predefined in the kernel, can be predefined in userspace code, and can be dynamically created (as “probes”) in kernel or userspace code. perf can do much more than just trace and count, though.

Which is the fastest cache mapping?

Associative Mapping
Associative Mapping – This means that the word id bits are used to identify which word in the block is needed, but the tag becomes all of the remaining bits. This enables the placement of any word at any place in the cache memory. It is considered to be the fastest and the most flexible mapping form.

Why does perf Stat not report cache misses?

According to perf tutorials, perf stat is supposed to report cache misses using hardware counters. However, on my system (up-to-date Arch Linux), it doesn’t:

What do you need to know about Perf in Linux?

PERF, which is part of the linux-tools package, is an infrastructure and suite of tools for collecting and analyzing performance data. You should install the version of PERF that matches the version of your Linux kernel.

How to count hardware performance events in PERF?

As a compromise, the L1-dcache-loads and L1-dcache-stores events are mapped to the ARMv7 data read/write L1 data cache event. You are likely to find similar compromises on other processor implementations, too. Each processor core has a set of hardware performance counters which count performance events.

Which is the best version of perf for Raspberry Pi?

You should install the version of PERF that matches the version of your Linux kernel. The data below were collected on a Raspberry Pi 2 (second generation, BCM2836 processor, ARMv7 Cortex-A7) using Raspbian Wheezy 3.18.9+v7+.