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McKenney" To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-trace-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, 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 , Frederic Weisbecker , 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 =?iso-8859-1?Q?Wei=DFschuh?= , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Yair Podemsky Subject: Re: [RFC PATCH v2 16/20] rcu: Make RCU dynticks counter size configurable Message-ID: Reply-To: paulmck@kernel.org References: <20230720163056.2564824-1-vschneid@redhat.com> <20230720163056.2564824-17-vschneid@redhat.com> <28d4abb7-8496-45ec-b270-ea2b6164537b@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: t1gxmefpr5wu1xzftxkhar9h6zbjsqtm X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0D7E61C0027 X-HE-Tag: 1689955755-834240 X-HE-Meta: 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 LxBXXal0 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 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 Fri, Jul 21, 2023 at 04:08:10PM +0100, Valentin Schneider wrote: > On 21/07/23 07:10, Paul E. McKenney wrote: > > On Fri, Jul 21, 2023 at 09:17:53AM +0100, Valentin Schneider wrote: > >> On 20/07/23 17:30, Valentin Schneider wrote: > >> > index bdd7eadb33d8f..1ff2aab24e964 100644 > >> > --- a/kernel/rcu/Kconfig > >> > +++ b/kernel/rcu/Kconfig > >> > @@ -332,4 +332,37 @@ config RCU_DOUBLE_CHECK_CB_TIME > >> > Say Y here if you need tighter callback-limit enforcement. > >> > Say N here if you are unsure. > >> > > >> > +config RCU_DYNTICKS_RANGE_BEGIN > >> > + int > >> > + depends on !RCU_EXPERT > >> > + default 31 if !CONTEXT_TRACKING_WORK > >> > >> You'll note that this should be 30 really, because the lower *2* bits are > >> taken by the context state (CONTEXT_GUEST has a value of 3). > >> > >> This highlights the fragile part of this: the Kconfig values are hardcoded, > >> but they depend on CT_STATE_SIZE, CONTEXT_MASK and CONTEXT_WORK_MAX. The > >> static_assert() will at least capture any misconfiguration, but having that > >> enforced by the actual Kconfig ranges would be less awkward. > >> > >> Do we currently have a way of e.g. making a Kconfig file depend on and use > >> values generated by a C header? > > > > Why not just have something like a boolean RCU_DYNTICKS_TORTURE Kconfig > > option and let the C code work out what the number of bits should be? > > > > I suppose that there might be a failure whose frequency depended on > > the number of bits, which might be an argument for keeping something > > like RCU_DYNTICKS_RANGE_BEGIN for fault isolation. But still using > > RCU_DYNTICKS_TORTURE for normal testing. > > > > Thoughts? > > > > AFAICT if we run tests with the minimum possible width, then intermediate > values shouldn't have much value. > > Your RCU_DYNTICKS_TORTURE suggestion sounds like a saner option than what I > came up with, as we can let the context tracking code figure out the widths > itself and not expose any of that to Kconfig. Agreed. If a need for variable numbers of bits ever does arise, we can worry about it at that time. And then we would have more information on what a variable-bit facility should look like. Thanx, Paul