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[84.229.251.248]) by smtp.gmail.com with ESMTPSA id k10-20020a5d6e8a000000b002d1daafea30sm13889142wrz.34.2023.03.22.07.11.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 07:11:46 -0700 (PDT) Message-ID: Subject: Re: [PATCH] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to MM CPUs From: ypodemsk@redhat.com To: Peter Zijlstra Cc: will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, npiggin@gmail.com, arnd@arndb.de, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com, ppandit@redhat.com, alougovs@redhat.com, David Hildenbrand Date: Wed, 22 Mar 2023 16:11:44 +0200 In-Reply-To: <20230320084902.GE2194297@hirez.programming.kicks-ass.net> References: <20230312080945.14171-1-ypodemsk@redhat.com> <20230320084902.GE2194297@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-18.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2023-03-20 at 09:49 +0100, Peter Zijlstra wrote: > On Sun, Mar 12, 2023 at 10:09:45AM +0200, Yair Podemsky wrote: > > Currently the tlb_remove_table_smp_sync IPI is sent to all CPUs > > indiscriminately, this causes unnecessary work and delays notable > > in > > real-time use-cases and isolated cpus, this patch will limit this > > IPI to > > only be sent to cpus referencing the effected mm and are currently > > in > > kernel space. > > Did you validate that all architectures for which this is relevant > actually set bits in mm_cpumask() ? > Hi Peter, Thank you for bringing this to my attention. I reviewed the architectures using the MMU_GATHER_RCU_TABLE_FREE: arm, powerpc, s390, sparc and x86 set the bit when switching process in. for arm64 removed set/clear bit in 38d96287504a ("arm64: mm: kill mm_cpumask usage") The reason given was that mm_cpumask was not used. Given that we now have a use for it, I will add a patch to revert. Thanks Yair