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[24.145.72.22]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-96916e5b10dsm2811280241.4.2026.06.27.10.49.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 27 Jun 2026 10:49:28 -0700 (PDT) From: Yury Norov X-Google-Original-From: Yury Norov Date: Sat, 27 Jun 2026 13:49:27 -0400 To: David Laight Cc: Robin Murphy , Andrew Morton , Rasmus Villemoes , Russell King , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Thomas Gleixner , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , "Rafael J. Wysocki" , Len Brown , Greg Kroah-Hartman , Danilo Krummrich , Chanwoo Choi , MyungJoo Ham , Kyungmin Park , Heiko Stuebner , Lorenzo Pieralisi , Xu Yilun , Tom Rix , Moritz Fischer , Yicong Yang , Jonathan Cameron , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny , Bjorn Helgaas , Shuai Xue , Will Deacon , Jiucheng Xu , Neil Armstrong , Kevin Hilman , Jerome Brunet , Martin Blumenstingl , Jing Zhang , Xu Yang , Linu Cherian , Gowthami Thiagarajan , Ji Sheng Teoh , Khuong Dinh , Daniel Lezcano , Zhang Rui , Lukasz Luba , Yury Norov , Kees Cook , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Aboorva Devarajan , "Ritesh Harjani (IBM)" , Ilkka Koskinen , Besar Wicaksono , Ma Ke , Chengwen Feng , linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-perf-users@vger.kernel.org, linux-acpi@vger.kernel.org, driver-core@lists.linux.dev, linux-pm@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-fpga@vger.kernel.org, linux-rdma@vger.kernel.org, nvdimm@lists.linux.dev, linux-pci@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-cxl@vger.kernel.org, linux-arm-msm@vger.kernel.org Subject: Re: [PATCH 13/16] perf: Use sysfs_emit() for cpumask show callbacks Message-ID: References: <20260528183625.870813-1-ynorov@nvidia.com> <20260528183625.870813-14-ynorov@nvidia.com> <7e980b99-1e4e-408b-8ebd-4d28116e7ad5@arm.com> <20260529130619.12f24264@pumpkin> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260529130619.12f24264@pumpkin> On Fri, May 29, 2026 at 01:06:19PM +0100, David Laight wrote: > On Fri, 29 May 2026 12:05:08 +0100 > Robin Murphy wrote: > > > On 2026-05-28 7:36 pm, Yury Norov wrote: > > > These callbacks are sysfs show paths. > > > > > > Use sysfs_emit() and cpumask_pr_args() to emit the masks. > > > > > > This prepares for removing cpumap_print_to_pagebuf(). > > > > TBH, looking at this diff I think it only shows the value of having a > > helper to abstract the boilerplate... > > > > I'm not sure I agree with the argument of removing something entirely > > just because it may occasionally be misused, but could we at least have > > something like: > > > > #define sysfs_emit_cpumask(buf, mask) \ > > sysfs_emit((buf), "%*pbl\n", cpumask_pr_args(mask)) > > > > to save the mess in all the many places where the current > > cpumap_print_to_pagebuf() usage _is_ entirely appropriate? This way you have to add 2 wrappers: #define sysfs_emit_cpulist(buf, mask) \ sysfs_emit((buf), "%*pbl\n", cpumask_pr_args(mask)) and #define sysfs_emit_cpumask(buf, mask) \ sysfs_emit((buf), "%*pb\n", cpumask_pr_args(mask)) There are people who complain even about DIV_ROUND_UP(), how hard it is to keep all that helpers in memory, and all that things. https://lore.kernel.org/all/20260304124805.GB2277644@noisy.programming.kicks-ass.net/ Disagree about DIV_ROUND_UP() (because yeah, I'm bad in math), but this sysfs_emit_cpumask() is a complete syntax redundancy. Once we have it, people will do this type of things: tmp = kmalloc(PAGE_SIZE); sysfs_emit_cpumask(tmp, mask); sysfs_emit(buf, "my prefix: %s\n", tmp); kfree(tmp); Patch #1 in this series is one example. My series that removes bitmap_print_to_pagebuf() will give you more: https://lore.kernel.org/all/20260303200842.124996-2-ynorov@nvidia.com/ It doesn't mean that *you* will misuse the API. It means that *I* will have to inspect the codebase for that type of bugs periodically. So, the overall state is simple: we've got well-established printf()-like functions that people know and understand, and we also have exotic APIs here and there with a non-standard interface and a clear potential to misuse. In this case, they have historical roots, but now we don't need them. > That has the advantage of letting you change how it is done (again) > without having to find all the callers. You mean things like silencing the prints or adding a prefix? If you believe that perf subsystem would benefit from it - that's OK. Just please keep it local. The kernel globally doesn't need to 'change how it is done' beyond the lib/vsprintf. The kernel really needs people to use something that the other people are familiar with. Thanks, Yury