From: Nicholas Piggin <npiggin@gmail.com>
Date: Fri, 3 Feb 2023 07:18:37 +0000 (+1000)
Subject: powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=77f68ebeee201e8960944863c03bd7ac613ca7ed;p=linux.git

powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN

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 b/arch/powerpc/Kconfig
index a6c4407d3ec83..49c6d36b2b3e6 100644
--- a/arch/powerpc/Kconfig
+++ 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