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Thu, 06 Apr 2023 07:11:59 -0700 (PDT) X-Google-Smtp-Source: AKy350YdFg9Rpod34ylmYUyAnCfxfiKdtnShPJSS+THNG9On45kotrwTmF6ARLq441OR3LQJbmn9Kg== X-Received: by 2002:a05:6214:c21:b0:5a2:e3e4:59b0 with SMTP id a1-20020a0562140c2100b005a2e3e459b0mr4151612qvd.44.1680790319253; Thu, 06 Apr 2023 07:11:59 -0700 (PDT) Received: from vschneid.remote.csb ([154.57.232.159]) by smtp.gmail.com with ESMTPSA id d11-20020a0cf6cb000000b005dd8b9345f4sm514523qvo.140.2023.04.06.07.11.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Apr 2023 07:11:58 -0700 (PDT) From: Valentin Schneider To: Peter Zijlstra Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode In-Reply-To: <20230406133805.GO386572@hirez.programming.kicks-ass.net> References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230405114148.GA351571@hirez.programming.kicks-ass.net> <20230406133805.GO386572@hirez.programming.kicks-ass.net> Date: Thu, 06 Apr 2023 15:11:52 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, dave.hansen@linux.intel.com, Yair Podemsky , sebastian.reichel@collabora.com, linux-mm@kvack.org, hpa@zytor.com, sparclinux@vger.kernel.org, agordeev@linux.ibm.com, will@kernel.org, ardb@kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, arnd@arndb.de, paulmck@kernel.org, aneesh.kumar@linux.ibm.com, x86@kernel.org, linux@armlinux.org.uk, mingo@redhat.com, samitolvanen@google.com, borntraeger@linux.ibm.com, hca@linux.ibm.com, keescook@chromium.org, gor@linux.ibm.com, Frederic Weisbecker , npiggin@gmail.com, rmk+kernel@armlinux.org.uk, bp@alien8.de, nick.hawkins@hpe.com, tglx@linutronix.de, jpoimboe@kernel.org, linux-arm-kernel@lists.infradead.org, alougovs@redhat.com, mtosatti@redhat.com, linux-kernel@vger.kernel.org, juerg.haefliger@canonical.com, svens@linux.ibm.com, dhildenb@redhat.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, davem@da vemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 06/04/23 15:38, Peter Zijlstra wrote: > On Wed, Apr 05, 2023 at 01:45:02PM +0100, Valentin Schneider wrote: >> >> I've been hacking on something like this (CSD deferral for NOHZ-full), >> and unfortunately this uses the CPU-local cfd_data storage thing, which >> means any further smp_call_function() from the same CPU to the same >> destination will spin on csd_lock_wait(), waiting for the target CPU to >> come out of userspace and flush the queue - and we've just spent extra >> effort into *not* disturbing it, so that'll take a while :( > > I'm not sure I buy into deferring stuff.. a NOHZ_FULL cpu might 'never' > come back. Queueing data just in case it does seems wasteful. Putting those callbacks straight into the bin would make my life much easier! Unfortunately, even if they really should, I don't believe all of the things being crammed onto NOHZ_FULL CPUs have the same definition of 'never' as we do :/