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Unified Memory Controller (UMC) events were introduced with Zen 4 as a part of the Performance Monitoring Version 2 (PerfMonV2) enhancements. An event is specified using the EventSelect bits and the RdWrMask bits can be used for additional filtering of read and write requests. As of now, a maximum of 12 channels of DDR5 are available on each socket and each channel is controlled by a dedicated UMC. Each UMC, in turn, has its own set of performance monitoring counters. Since the MSR address space for the UMC PERF_CTL and PERF_CTR registers are reused across sockets, uncore groups are created on the basis of socket IDs. Hence, group exclusivity is mandatory while opening events so that events for an UMC can only be opened on CPUs which are on the same socket as the corresponding memory channel. For each socket, the total number of available UMC counters and active memory channels are determined from CPUID leaf 0x80000022 EBX and ECX respectively. Usually, on Zen 4, each UMC has four counters. MSR assignments are determined on the basis of active UMCs. E.g. if UMCs 1, 4 and 9 are active for a given socket, then * UMC 1 gets MSRs 0xc0010800 to 0xc0010807 as PERF_CTLs and PERF_CTRs * UMC 4 gets MSRs 0xc0010808 to 0xc001080f as PERF_CTLs and PERF_CTRs * UMC 9 gets MSRs 0xc0010810 to 0xc0010817 as PERF_CTLs and PERF_CTRs If there are sockets without any online CPUs when the amd_uncore driver is loaded, UMCs for such sockets will not be discoverable since the mechanism relies on executing the CPUID instruction on an online CPU from the socket. Signed-off-by: Sandipan Das <sandipan.das@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/b25f391205c22733493abec1ed850b71784edc5f.1696425185.git.sandipan.das@amd.com |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.