+ powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch added to mm-unstable branch

+ powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN
has been added to the -mm mm-unstable branch.  Its filename is
     powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Nicholas Piggin <npiggin@gmail.com>
Subject: powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN
Date: Fri, 3 Feb 2023 17:18:37 +1000

On a 16-socket 192-core POWER8 system, the context_switch1_threads
benchmark from will-it-scale (see earlier changelog), upstream can achieve
a rate of about 1 million context switches per second, due to contention
on the mm refcount.

64s meets the prerequisites for CONFIG_MMU_LAZY_TLB_SHOOTDOWN, so enable
the option.  This increases the above benchmark to 118 million context
switches per second.

This generates 314 additional IPI interrupts on a 144 CPU system doing a
kernel compile, which is in the noise in terms of kernel cycles.

Link: https://lkml.kernel.org/r/20230203071837.1136453-6-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


diff --git a/arch/powerpc/Kconfig~powerpc-64s-enable-mmu_lazy_tlb_shootdown b/arch/powerpc/Kconfig
--- a/arch/powerpc/Kconfig~powerpc-64s-enable-mmu_lazy_tlb_shootdown
+++ b/arch/powerpc/Kconfig
@@ -266,6 +266,7 @@ config PPC
 	select MMU_GATHER_PAGE_SIZE
 	select MMU_GATHER_RCU_TABLE_FREE
 	select MMU_GATHER_MERGE_VMAS
+	select MMU_LAZY_TLB_SHOOTDOWN		if PPC_BOOK3S_64
 	select MODULES_USE_ELF_RELA
 	select NEED_DMA_MAP_STATE		if PPC64 || NOT_COHERENT_CACHE
 	select NEED_PER_CPU_EMBED_FIRST_CHUNK	if PPC64
_

Patches currently in -mm which might be from npiggin@gmail.com are

kthread-simplify-kthread_use_mm-refcounting.patch
lazy-tlb-introduce-lazy-tlb-mm-refcount-helper-functions.patch
lazy-tlb-allow-lazy-tlb-mm-refcounting-to-be-configurable.patch
lazy-tlb-shoot-lazies-non-refcounting-lazy-tlb-mm-reference-handling-scheme.patch
powerpc-64s-enable-mmu_lazy_tlb_shootdown.patch