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Kan Liang cdf7658ea2 perf/x86/intel: Use better start period for frequency mode 
[ Upstream commit a26b24b2e2 ]

Freqency mode is the current default mode of Linux perf. A period of 1 is
used as a starting period. The period is auto-adjusted on each tick or an
overflow, to meet the frequency target.

The start period of 1 is too low and may trigger some issues:

- Many HWs do not support period 1 well.
  https://lore.kernel.org/lkml/875xs2oh69.ffs@tglx/

- For an event that occurs frequently, period 1 is too far away from the
  real period. Lots of samples are generated at the beginning.
  The distribution of samples may not be even.

- A low starting period for frequently occurring events also challenges
  virtualization, which has a longer path to handle a PMI.

The limit_period value only checks the minimum acceptable value for HW.
It cannot be used to set the start period, because some events may
need a very low period. The limit_period cannot be set too high. It
doesn't help with the events that occur frequently.

It's hard to find a universal starting period for all events. The idea
implemented by this patch is to only give an estimate for the popular
HW and HW cache events. For the rest of the events, start from the lowest
possible recommended value.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250117151913.3043942-3-kan.liang@linux.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-03-22 12:50:44 -07:00
arch perf/x86/intel: Use better start period for frequency mode 2025-03-22 12:50:44 -07:00
block block: fix conversion of GPT partition name to 7-bit 2025-03-13 12:58:27 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: ecc - Prevent ecc_digits_from_bytes from reading too many bytes 2025-01-09 13:31:52 +01:00
Documentation sched/isolation: Prevent boot crash when the boot CPU is nohz_full 2025-03-22 12:50:37 -07:00
drivers drm/vkms: Round fixp2int conversion in lerp_u16 2025-03-22 12:50:44 -07:00
fs fuse: don't truncate cached, mutated symlink 2025-03-22 12:50:44 -07:00
include fuse: don't truncate cached, mutated symlink 2025-03-22 12:50:44 -07:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-09 10:32:46 +01:00
io_uring io-wq: backoff when retrying worker creation 2025-03-22 12:50:43 -07:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-09 10:32:54 +01:00
kernel sched: Clarify wake_up_q()'s write to task->wake_q.next 2025-03-22 12:50:41 -07:00
lib rcuref: Plug slowpath race in rcuref_put() 2025-03-07 16:45:47 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: hugetlb: Add huge page size param to huge_ptep_get_and_clear() 2025-03-13 12:58:38 +01:00
net sctp: Fix undefined behavior in left shift operation 2025-03-22 12:50:43 -07:00
rust rust: init: use explicit ABI to clean warning in future compilers 2025-02-17 09:40:27 +01:00
samples samples/landlock: Fix possible NULL dereference in parse_path() 2025-02-08 09:51:57 +01:00
scripts scripts/gdb: fix aarch64 userspace detection in get_current_task 2025-02-17 09:40:39 +01:00
security ima: Reset IMA_NONACTION_RULE_FLAGS after post_setattr 2025-03-13 12:58:40 +01:00
sound ASoC: tas2764: Set the SDOUT polarity correctly 2025-03-22 12:50:44 -07:00
tools selftests/bpf: Fix invalid flag of recv() 2025-03-22 12:50:42 -07:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 12:58:38 +01:00
virt KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock 2024-10-04 16:29:47 +02:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-04 16:29:44 +02:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS membarrier: riscv: Add full memory barrier in switch_mm() 2024-09-12 11:11:45 +02:00
Makefile Linux 6.6.83 2025-03-13 12:58:41 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.