From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yury Norov Date: Sun, 28 Nov 2021 06:34:47 +0000 Subject: Re: [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le} Message-Id: <20211128063447.GA270945@lapt> List-Id: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Cc: linux-kernel@vger.kernel.org, "James E.J. Bottomley" , "Martin K. Petersen" , "Paul E. McKenney" , "Rafael J. Wysocki" , Alexander Shishkin , Alexey Klimov , Amitkumar Karwar , Andi Kleen , Andrew Lunn , Andrew Morton , Andy Gross , Andy Lutomirski , Andy Shevchenko , Anup Patel , Ard Biesheuvel , Arnaldo Carvalho de Melo , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christoph Hellwig , Christoph Lameter , Daniel Vetter , Dave Hansen , David Airlie , David Laight , Dennis Zhou , Dinh Nguyen , Geetha sowjanya , Geert Uytterhoeven , Greg Kroah-Hartman , Guo Ren , Hans de Goede , Heiko Carstens , Ian Rogers , Ingo Molnar , Jakub Kicinski , Jason Wessel , Jens Axboe , Jiri Olsa , Jonathan Cameron , Juri Lelli , Kalle Valo , Kees Cook , Krzysztof Kozlowski , Lee Jones , Marc Zyngier , Marcin Wojtas , Mark Gross , Mark Rutland , Matti Vaittinen , Mauro Carvalho Chehab , Mel Gorman , Michael Ellerman , Mike Marciniszyn , Nicholas Piggin , Palmer Dabbelt , Peter Zijlstra , Petr Mladek , Randy Dunlap , Rasmus Villemoes , Roy Pledge , Russell King , Saeed Mahameed , Sagi Grimberg , Sergey Senozhatsky , Solomon Peachy , Stephen Boyd , Stephen Rothwell , Steven Rostedt , Subbaraya Sundeep , Sudeep Holla , Sunil Goutham , Tariq Toukan , Tejun Heo , Thomas Bogendoerfer , Thomas Gleixner , Ulf Hansson , Vincent Guittot , Vineet Gupta , Viresh Kumar , Vivien Didelot , Vlastimil Babka , Will Deacon , bcm-kernel-feedback-list@broadcom.com, kvm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-csky@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, linuxppc-dev@lists.ozlabs.org (restore CC list) On Sun, Nov 28, 2021 at 05:56:51AM +0100, Michał Mirosław wrote: > On Sat, Nov 27, 2021 at 07:57:02PM -0800, Yury Norov wrote: > > Add num_{possible,present,active}_cpus_{eq,gt,le} and replace num_*_cpus() > > with one of new functions where appropriate. This allows num_*_cpus_*() > > to return earlier depending on the condition. > [...] > > @@ -3193,7 +3193,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size, > > > > /* allocate pages */ > > j = 0; > > - for (unit = 0; unit < num_possible_cpus(); unit++) { > > + for (unit = 0; num_possible_cpus_gt(unit); unit++) { > > This looks dubious. Only this? > The old version I could hope the compiler would call > num_possible_cpus() only once if it's marked const or pure, but the > alternative is going to count the bits every time making this a guaranteed > O(n^2) even though the bitmap doesn't change. num_possible_cpus() is not const neither pure. This is O(n^2) before and after.