From: Brian Gerst Date: Mon, 3 Mar 2025 16:52:36 +0000 (-0500) Subject: percpu: Introduce percpu hot section X-Git-Tag: v6.15-rc1~216^2~84 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ab2bb9c084f7e3b641ceba91efc33b3adcd1846e;p=thirdparty%2Fkernel%2Flinux.git percpu: Introduce percpu hot section Add a subsection to the percpu data for frequently accessed variables that should remain cached on each processor. These varables should not be accessed from other processors to avoid cacheline bouncing. This will replace the pcpu_hot struct on x86, and open up similar functionality to other architectures and the kernel core. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Acked-by: Uros Bizjak Cc: Linus Torvalds Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20250303165246.2175811-2-brgerst@gmail.com --- diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index b32e453acf9d3..c4e8fac502543 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -385,6 +385,11 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) . = ALIGN(PAGE_SIZE); \ __nosave_end = .; +#define CACHE_HOT_DATA(align) \ + . = ALIGN(align); \ + *(SORT_BY_ALIGNMENT(.data..hot.*)) \ + . = ALIGN(align); + #define PAGE_ALIGNED_DATA(page_align) \ . = ALIGN(page_align); \ *(.data..page_aligned) \ @@ -1065,6 +1070,11 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) . = ALIGN(PAGE_SIZE); \ *(.data..percpu..page_aligned) \ . = ALIGN(cacheline); \ + __per_cpu_hot_start = .; \ + *(SORT_BY_ALIGNMENT(.data..percpu..hot.*)) \ + __per_cpu_hot_pad = .; \ + . = ALIGN(cacheline); \ + __per_cpu_hot_end = .; \ *(.data..percpu..read_mostly) \ . = ALIGN(cacheline); \ *(.data..percpu) \ @@ -1112,6 +1122,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) INIT_TASK_DATA(inittask) \ NOSAVE_DATA \ PAGE_ALIGNED_DATA(pagealigned) \ + CACHE_HOT_DATA(cacheline) \ CACHELINE_ALIGNED_DATA(cacheline) \ READ_MOSTLY_DATA(cacheline) \ DATA_DATA \ diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h index 40d34e032d5b8..0fcacb9097789 100644 --- a/include/linux/percpu-defs.h +++ b/include/linux/percpu-defs.h @@ -112,6 +112,19 @@ #define DEFINE_PER_CPU(type, name) \ DEFINE_PER_CPU_SECTION(type, name, "") +/* + * Declaration/definition used for per-CPU variables that are frequently + * accessed and should be in a single cacheline. + * + * For use only by architecture and core code. Only use scalar or pointer + * types to maximize density. + */ +#define DECLARE_PER_CPU_CACHE_HOT(type, name) \ + DECLARE_PER_CPU_SECTION(type, name, "..hot.." #name) + +#define DEFINE_PER_CPU_CACHE_HOT(type, name) \ + DEFINE_PER_CPU_SECTION(type, name, "..hot.." #name) + /* * Declaration/definition used for per-CPU variables that must be cacheline * aligned under SMP conditions so that, whilst a particular instance of the