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[213.44.141.166]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d43812ab11sm12976636d6.94.2024.11.20.09.10.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Nov 2024 09:10:56 -0800 (PST) From: Valentin Schneider To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, x86@kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, Nicolas Saenz Julienne , Steven Rostedt , Masami Hiramatsu , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Peter Zijlstra , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?utf-8?Q?Wei=C3=9Fschuh?= , Juri Lelli , Marcelo Tosatti , Yair Podemsky , Daniel Wagner , Petr Tesarik Subject: Re: [RFC PATCH v3 11/15] context-tracking: Introduce work deferral infrastructure In-Reply-To: References: <20241119153502.41361-1-vschneid@redhat.com> <20241119153502.41361-12-vschneid@redhat.com> Date: Wed, 20 Nov 2024 18:10:43 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: gB_oW5o7TkrORpW1QjbbIgC_JLM9d-FDe7s9GDBlIPo_1732122658 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Server: rspam10 X-Stat-Signature: rb1678bcdyw8qa5tjbbh55a131dkqabp X-Rspamd-Queue-Id: 682B3A0008 X-Rspam-User: X-HE-Tag: 1732122623-272334 X-HE-Meta: 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 6+EFcr5I d7Lbuuqta+mdjigjK7fu0ynOX0o0YBUXHJoguLjln2zje0qYAzmUsP8QFLUslx0yKn0aURz1aLfdISR34D/zm2HbcJbzpyXKTgEOTa6Yv5GE4bc+UI6xglDyz59gpQaeJcJur+NYtonfTRanITNKeGy/5fONd8vBmt09scFm4Nk0z132af2mwCmlGF+suk1ZiekP2kZIkz2C5Z5CdNPOBb8LAS7dtkWQnVK35s/Ha905mjvZIanECZAzUT/LJE+KgFUMa+tF7HhiycyAR3A2M5DcBJam+pYgGGOLzQV4xlh2imqCIN5gbe52p+SsFYwc85AWKXXnyW+R935GyGzWRPERm2aDW8w8kDGLYXvivHWxiGANOXsUaBVZYvBhPcQyiBjaM 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: List-Subscribe: List-Unsubscribe: On 20/11/24 15:23, Frederic Weisbecker wrote: > Ah but there is CT_STATE_GUEST and I see the last patch also applies that to > CT_STATE_IDLE. > > So that could be: > > bool ct_set_cpu_work(unsigned int cpu, unsigned int work) > { > struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); > unsigned int old; > bool ret = false; > > preempt_disable(); > > old = atomic_read(&ct->state); > > /* CT_STATE_IDLE can be added to last patch here */ > if (!(old & (CT_STATE_USER | CT_STATE_GUEST))) { > old &= ~CT_STATE_MASK; > old |= CT_STATE_USER; > } Hmph, so that lets us leverage the cmpxchg for a !CT_STATE_KERNEL check, but we get an extra loop if the target CPU exits kernelspace not to userspace (e.g. vcpu or idle) in the meantime - not great, not terrible. At the cost of one extra bit for the CT_STATE area, with CT_STATE_KERNEL=1 we could do: old = atomic_read(&ct->state); old &= ~CT_STATE_KERNEL;