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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 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, mtosatti@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 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-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BD4D220025 X-Stat-Signature: 7zjzeqi6owshzu48i39fx5sqbh46i99x X-Rspam-User: X-HE-Tag: 1680790322-762824 X-HE-Meta: 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 rzHxxEV1 KeUxW4qS8Jeq973NwiC64homMnCucQS0hGqBusqCskuw49t5rhhriMT8JzZBAZnRO4wCNri1xI1DbFD7iY763AwfcwhOEFwBDdRQMu4TcGOMtEucluQ9LhrojfNaDGmif4Tx6HoL7ol+z2vOSOsU1HKvDWNxUGRSDGod8FwtMAyAeXYDjWtOdmo682aVCXlSa/qTyJ4jxz4FTUNQjzd2U1tpD1w+/ISByobeTNm4AygMsi4LISC1RuodL678zubA4vgYjFJADAF+maeTcdI0x3jAIehGe0k62XGCble3AC9oDtBC3IEQ/pq4ogrokUHOT0/dBaoy69JYEl4NfqHqM9XycnSoWtALUlhzN5wcPuuoIYPftMF9beLc71WfyhS92sc51MVASIm3nAAcrkb7tEZg4PNERZeNcxEhpr+dxbucHJJU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000008, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 :/