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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pk9De-00A4Ht-2h; Wed, 05 Apr 2023 19:54:59 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B6577300194; Wed, 5 Apr 2023 21:54:57 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9929B200B42A8; Wed, 5 Apr 2023 21:54:57 +0200 (CEST) Date: Wed, 5 Apr 2023 21:54:57 +0200 From: Peter Zijlstra To: Marcelo Tosatti Cc: Frederic Weisbecker , Yair Podemsky , linux@armlinux.org.uk, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, ardb@kernel.org, juerg.haefliger@canonical.com, rmk+kernel@armlinux.org.uk, geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, sebastian.reichel@collabora.com, nick.hawkins@hpe.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, vschneid@redhat.com, dhildenb@redhat.com, alougovs@redhat.com Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Message-ID: <20230405195457.GC365912@hirez.programming.kicks-ass.net> References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 11D86100010 X-Stat-Signature: tsj9ps8botqcdtiee8kicjpbtpdpe9dg X-HE-Tag: 1680724563-858215 X-HE-Meta: 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 mr6sEAOi lQCJnn700n6cvLhPu2Ap90P7MwcOkDyj8qT1wn0nxcYzeJ7FGTgy6D0maVTo3GLyVYeE4mPgZUEhDXRxtj/TQ9Kn5rDzUAGphTWS+XvUw4y5beiZ/ANPN+/GTrsPtPDspvMRSGbWlD1PapB5PCcdmIZm5fkB8JrPbBMpgc+kjaHMi6rOicUExNhFJWfDmiW7Kryt1nJvX+yWKnOncG9agARDqRLzVoNmnLYwk5ByvRhBLT24dSKmqfwhNIGnXoLoNX14bfr+UUpNhXHAjRtrBmnWXrNJ3DYDtdOHV 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 Wed, Apr 05, 2023 at 04:43:14PM -0300, Marcelo Tosatti wrote: > Two points: > > 1) For a virtualized system, the overhead is not only of executing the > IPI but: > > VM-exit > run VM-exit code in host > handle IPI > run VM-entry code in host > VM-entry I thought we could do IPIs without VMexit these days? Also virt... /me walks away. > 2) Depends on the application and the definition of "occasional". > > For certain types of applications (for example PLC software or > RAN processing), upon occurrence of an event, it is necessary to > complete a certain task in a maximum amount of time (deadline). If the application is properly NOHZ_FULL and never does a kernel entry, it will never get that IPI. If it is a pile of shit and does kernel entries while it pretends to be NOHZ_FULL it gets to keep the pieces and no amount of crying will get me to care.