Merge tag 'timers-core-2024-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer updates from Thomas Gleixner:
 "A large set of updates and features for timers and timekeeping:

   - The hierarchical timer pull model

     When timer wheel timers are armed they are placed into the timer
     wheel of a CPU which is likely to be busy at the time of expiry.
     This is done to avoid wakeups on potentially idle CPUs.

     This is wrong in several aspects:

       1) The heuristics to select the target CPU are wrong by
          definition as the chance to get the prediction right is
          close to zero.

       2) Due to #1 it is possible that timers are accumulated on
          a single target CPU

       3) The required computation in the enqueue path is just overhead
          for dubious value especially under the consideration that the
          vast majority of timer wheel timers are either canceled or
          rearmed before they expire.

     The timer pull model avoids the above by removing the target
     computation on enqueue and queueing timers always on the CPU on
     which they get armed.

     This is achieved by having separate wheels for CPU pinned timers
     and global timers which do not care about where they expire.

     As long as a CPU is busy it handles both the pinned and the global
     timers which are queued on the CPU local timer wheels.

     When a CPU goes idle it evaluates its own timer wheels:

       - If the first expiring timer is a pinned timer, then the global
         timers can be ignored as the CPU will wake up before they
         expire.

       - If the first expiring timer is a global timer, then the expiry
         time is propagated into the timer pull hierarchy and the CPU
         makes sure to wake up for the first pinned timer.

     The timer pull hierarchy organizes CPUs in groups of eight at the
     lowest level and at the next levels groups of eight groups up to
     the point where no further aggregation of groups is required, i.e.
     the number of levels is log8(NR_CPUS). The magic number of eight
     has been established by experimention, but can be adjusted if
     needed.

     In each group one busy CPU acts as the migrator. It's only one CPU
     to avoid lock contention on remote timer wheels.

     The migrator CPU checks in its own timer wheel handling whether
     there are other CPUs in the group which have gone idle and have
     global timers to expire. If there are global timers to expire, the
     migrator locks the remote CPU timer wheel and handles the expiry.

     Depending on the group level in the hierarchy this handling can
     require to walk the hierarchy downwards to the CPU level.

     Special care is taken when the last CPU goes idle. At this point
     the CPU is the systemwide migrator at the top of the hierarchy and
     it therefore cannot delegate to the hierarchy. It needs to arm its
     own timer device to expire either at the first expiring timer in
     the hierarchy or at the first CPU local timer, which ever expires
     first.

     This completely removes the overhead from the enqueue path, which
     is e.g. for networking a true hotpath and trades it for a slightly
     more complex idle path.

     This has been in development for a couple of years and the final
     series has been extensively tested by various teams from silicon
     vendors and ran through extensive CI.

     There have been slight performance improvements observed on network
     centric workloads and an Intel team confirmed that this allows them
     to power down a die completely on a mult-die socket for the first
     time in a mostly idle scenario.

     There is only one outstanding ~1.5% regression on a specific
     overloaded netperf test which is currently investigated, but the
     rest is either positive or neutral performance wise and positive on
     the power management side.

   - Fixes for the timekeeping interpolation code for cross-timestamps:

     cross-timestamps are used for PTP to get snapshots from hardware
     timers and interpolated them back to clock MONOTONIC. The changes
     address a few corner cases in the interpolation code which got the
     math and logic wrong.

   - Simplifcation of the clocksource watchdog retry logic to
     automatically adjust to handle larger systems correctly instead of
     having more incomprehensible command line parameters.

   - Treewide consolidation of the VDSO data structures.

   - The usual small improvements and cleanups all over the place"

* tag 'timers-core-2024-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (62 commits)
  timer/migration: Fix quick check reporting late expiry
  tick/sched: Fix build failure for CONFIG_NO_HZ_COMMON=n
  vdso/datapage: Quick fix - use asm/page-def.h for ARM64
  timers: Assert no next dyntick timer look-up while CPU is offline
  tick: Assume timekeeping is correctly handed over upon last offline idle call
  tick: Shut down low-res tick from dying CPU
  tick: Split nohz and highres features from nohz_mode
  tick: Move individual bit features to debuggable mask accesses
  tick: Move got_idle_tick away from common flags
  tick: Assume the tick can't be stopped in NOHZ_MODE_INACTIVE mode
  tick: Move broadcast cancellation up to CPUHP_AP_TICK_DYING
  tick: Move tick cancellation up to CPUHP_AP_TICK_DYING
  tick: Start centralizing tick related CPU hotplug operations
  tick/sched: Don't clear ts::next_tick again in can_stop_idle_tick()
  tick/sched: Rename tick_nohz_stop_sched_tick() to tick_nohz_full_stop_tick()
  tick: Use IS_ENABLED() whenever possible
  tick/sched: Remove useless oneshot ifdeffery
  tick/nohz: Remove duplicate between lowres and highres handlers
  tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()
  hrtimer: Select housekeeping CPU during migration
  ...

13 files changed, 12 insertions, 76 deletions

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index d68101655b74..9f21e170320f 100644
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -4,7 +4,6 @@
 
 #include <asm/auxvec.h>
 #include <asm/hwcap.h>
-#include <asm/vdso_datapage.h>
 
 /*
  * ELF register definitions..
diff --git a/arch/arm/include/asm/vdso_datapage.h b/arch/arm/include/asm/vdso_datapage.h
deleted file mode 100644
index bef68f59928d..000000000000
--- a/arch/arm/include/asm/vdso_datapage.h
+++ /dev/null
@@ -1,26 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Adapted from arm64 version.
- *
- * Copyright (C) 2012 ARM Limited
- */
-#ifndef __ASM_VDSO_DATAPAGE_H
-#define __ASM_VDSO_DATAPAGE_H
-
-#ifdef __KERNEL__
-
-#ifndef __ASSEMBLY__
-
-#include <vdso/datapage.h>
-#include <asm/page.h>
-
-union vdso_data_store {
-	struct vdso_data	data[CS_BASES];
-	u8			page[PAGE_SIZE];
-};
-
-#endif /* !__ASSEMBLY__ */
-
-#endif /* __KERNEL__ */
-
-#endif /* __ASM_VDSO_DATAPAGE_H */
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 219cbc7e5d13..4915662842ff 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -21,10 +21,12 @@
 #include <asm/mpu.h>
 #include <asm/procinfo.h>
 #include <asm/suspend.h>
-#include <asm/vdso_datapage.h>
 #include <asm/hardware/cache-l2x0.h>
 #include <linux/kbuild.h>
 #include <linux/arm-smccc.h>
+
+#include <vdso/datapage.h>
+
 #include "signal.h"
 
 /*
diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
index f297d66a8a76..d499ad461b00 100644
--- a/arch/arm/kernel/vdso.c
+++ b/arch/arm/kernel/vdso.c
@@ -21,7 +21,6 @@
 #include <asm/cacheflush.h>
 #include <asm/page.h>
 #include <asm/vdso.h>
-#include <asm/vdso_datapage.h>
 #include <clocksource/arm_arch_timer.h>
 #include <vdso/helpers.h>
 #include <vdso/vsyscall.h>
@@ -35,9 +34,6 @@ extern char vdso_start[], vdso_end[];
 /* Total number of pages needed for the data and text portions of the VDSO. */
 unsigned int vdso_total_pages __ro_after_init;
 
-/*
- * The VDSO data page.
- */
 static union vdso_data_store vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = vdso_data_store.data;
 
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 5562daf38a22..89b6e7840002 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -69,10 +69,7 @@ static struct vdso_abi_info vdso_info[] __ro_after_init = {
 /*
  * The vDSO data page.
  */
-static union {
-	struct vdso_data	data[CS_BASES];
-	u8			page[PAGE_SIZE];
-} vdso_data_store __page_aligned_data;
+static union vdso_data_store vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = vdso_data_store.data;
 
 static int vdso_mremap(const struct vm_special_mapping *sm,
diff --git a/arch/csky/include/asm/vdso.h b/arch/csky/include/asm/vdso.h
index bdce581b5fcb..181a15edafe8 100644
--- a/arch/csky/include/asm/vdso.h
+++ b/arch/csky/include/asm/vdso.h
@@ -5,11 +5,6 @@
 
 #include <linux/types.h>
 
-#ifndef GENERIC_TIME_VSYSCALL
-struct vdso_data {
-};
-#endif
-
 /*
  * The VDSO symbols are mapped into Linux so we can just use regular symbol
  * addressing to get their offsets in userspace.  The symbols are mapped at an
diff --git a/arch/csky/kernel/vdso.c b/arch/csky/kernel/vdso.c
index 16c20d64d165..2ca886e4a458 100644
--- a/arch/csky/kernel/vdso.c
+++ b/arch/csky/kernel/vdso.c
@@ -8,25 +8,15 @@
 #include <linux/slab.h>
 
 #include <asm/page.h>
-#ifdef GENERIC_TIME_VSYSCALL
 #include <vdso/datapage.h>
-#else
-#include <asm/vdso.h>
-#endif
 
 extern char vdso_start[], vdso_end[];
 
 static unsigned int vdso_pages;
 static struct page **vdso_pagelist;
 
-/*
- * The vDSO data page.
- */
-static union {
-	struct vdso_data	data;
-	u8			page[PAGE_SIZE];
-} vdso_data_store __page_aligned_data;
-struct vdso_data *vdso_data = &vdso_data_store.data;
+static union vdso_data_store vdso_data_store __page_aligned_data;
+struct vdso_data *vdso_data = vdso_data_store.data;
 
 static int __init vdso_init(void)
 {
diff --git a/arch/loongarch/kernel/vdso.c b/arch/loongarch/kernel/vdso.c
index 14941e4be66d..90dfccb41c14 100644
--- a/arch/loongarch/kernel/vdso.c
+++ b/arch/loongarch/kernel/vdso.c
@@ -21,15 +21,13 @@
 #include <asm/vdso.h>
 #include <vdso/helpers.h>
 #include <vdso/vsyscall.h>
+#include <vdso/datapage.h>
 #include <generated/vdso-offsets.h>
 
 extern char vdso_start[], vdso_end[];
 
 /* Kernel-provided data used by the VDSO. */
-static union {
-	u8 page[PAGE_SIZE];
-	struct vdso_data data[CS_BASES];
-} generic_vdso_data __page_aligned_data;
+static union vdso_data_store generic_vdso_data __page_aligned_data;
 
 static union {
 	u8 page[LOONGARCH_VDSO_DATA_SIZE];
diff --git a/arch/mips/include/asm/vdso.h b/arch/mips/include/asm/vdso.h
index cc7b516129a8..afb03d45bcd0 100644
--- a/arch/mips/include/asm/vdso.h
+++ b/arch/mips/include/asm/vdso.h
@@ -50,9 +50,4 @@ extern struct mips_vdso_image vdso_image_o32;
 extern struct mips_vdso_image vdso_image_n32;
 #endif
 
-union mips_vdso_data {
-	struct vdso_data data[CS_BASES];
-	u8 page[PAGE_SIZE];
-};
-
 #endif /* __ASM_VDSO_H */
diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
index f6d40e43f108..dda36fa26307 100644
--- a/arch/mips/kernel/vdso.c
+++ b/arch/mips/kernel/vdso.c
@@ -24,7 +24,7 @@
 #include <vdso/vsyscall.h>
 
 /* Kernel-provided data used by the VDSO. */
-static union mips_vdso_data mips_vdso_data __page_aligned_data;
+static union vdso_data_store mips_vdso_data __page_aligned_data;
 struct vdso_data *vdso_data = mips_vdso_data.data;
 
 /*
diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
index 2cf76218a5bd..98315b98256d 100644
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -30,14 +30,8 @@ enum rv_vdso_map {
 
 #define VVAR_SIZE  (VVAR_NR_PAGES << PAGE_SHIFT)
 
-/*
- * The vDSO data page.
- */
-static union {
-	struct vdso_data	data;
-	u8			page[PAGE_SIZE];
-} vdso_data_store __page_aligned_data;
-struct vdso_data *vdso_data = &vdso_data_store.data;
+static union vdso_data_store vdso_data_store __page_aligned_data;
+struct vdso_data *vdso_data = vdso_data_store.data;
 
 struct __vdso_info {
 	const char *name;
diff --git a/arch/s390/include/asm/vdso/data.h b/arch/s390/include/asm/vdso/data.h
index 73ee89142666..0e2b40ef69b0 100644
--- a/arch/s390/include/asm/vdso/data.h
+++ b/arch/s390/include/asm/vdso/data.h
@@ -3,7 +3,6 @@
 #define __S390_ASM_VDSO_DATA_H
 
 #include <linux/types.h>
-#include <vdso/datapage.h>
 
 struct arch_vdso_data {
 	__s64 tod_steering_delta;
diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index bbaefd84f15e..a45b3a4c91db 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -25,10 +25,7 @@ extern char vdso32_start[], vdso32_end[];
 
 static struct vm_special_mapping vvar_mapping;
 
-static union {
-	struct vdso_data	data[CS_BASES];
-	u8			page[PAGE_SIZE];
-} vdso_data_store __page_aligned_data;
+static union vdso_data_store vdso_data_store __page_aligned_data;
 
 struct vdso_data *vdso_data = vdso_data_store.data;