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bh=58rHNWziKG5F+1xvClRR26TGR/kzgtphh1+ss0F3o1k=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=UiT+0xxuBn3xEDjfKMhE+S6nA/FuZ+LuP5xkiXmr+Z26p7zBTGouYiQnhVvpMNQe4 72VgieV739lydXF/yzCq6+namJMMvgD8JJR9Z49ozGh6Bsy6ZoXgzNAL7cPtbQkAKe Yw2Hdqhy91RjOwm5mv0YwB7I/7qyguOod5YPTNVs= Date: Sun, 26 Feb 2023 14:12:38 -0800 From: Andrew Morton To: Nicholas Piggin Cc: Linus Torvalds , Nadav Amit , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Rik van Riel , linux-arch@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v7 5/5] powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN Message-Id: <20230226141238.6ec5fdf7d75dcf2cd4c58ba0@linux-foundation.org> In-Reply-To: <20230203071837.1136453-6-npiggin@gmail.com> References: <20230203071837.1136453-1-npiggin@gmail.com> <20230203071837.1136453-6-npiggin@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7BC271C0013 X-Rspam-User: X-Stat-Signature: poa77ctew5475ukzx41ac67pgy78445u X-HE-Tag: 1677449561-314944 X-HE-Meta: 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 ZQqlx9Y2 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 3 Feb 2023 17:18:37 +1000 Nicholas Piggin wrote: > 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. Is that the best you can do ;) > 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. > > ... > > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -265,6 +265,7 @@ 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 Can we please have a summary of which other architectures might benefit from this, and what must they do? As this is powerpc-only, I expect it won't get a lot of testing in mm.git or in linux-next. The powerpc maintainers might choose to merge in the mm-stable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm if this is a concern.