On Tue, Nov 28, 2023 at 02:37:22PM +0000, Jonathan Cameron wrote: > On Tue, 07 Nov 2023 10:29:23 +0000 > Russell King <rmk+kernel@xxxxxxxxxxxxxxx> wrote: > > > From: James Morse <james.morse@xxxxxxx> > > > > register_cpu_capacity_sysctl() adds a property to sysfs that describes > > the CPUs capacity. This is done from a subsys_initcall() that assumes > > all possible CPUs are registered. > > > > With CPU hotplug, possible CPUs aren't registered until they become > > present, (or for arm64 enabled). This leads to messages during boot: > > | register_cpu_capacity_sysctl: too early to get CPU1 device! > > and once these CPUs are added to the system, the file is missing. > > > > Move this to a cpuhp callback, so that the file is created once > > CPUs are brought online. This covers CPUs that are added late by > > mechanisms like hotplug. > > One observable difference is the file is now missing for offline CPUs. > > > > Signed-off-by: James Morse <james.morse@xxxxxxx> > > --- > > If the offline CPUs thing is a problem for the tools that consume > > this value, we'd need to move cpu_capacity to be part of cpu.c's > > common_cpu_attr_groups. > > I'm not keen on squirting sysfs files in from code so > might be nice to do that anyway and use is_visible() / sysfs_update_group() > but that would be a job for another day if at all. I'm doing my best, but it's really not helped by the dysfunctional nature of some parts of the kernel community. I have now decided that this is not possible to implement. So while it's a nice idea, I don't think we'll ever see it. As I mentioned on the 14th November, complete with a patch (and got no response from anyone): > Looking into doing this, the easy bit is adding the attribute group > with an appropriate .is_visible dependent on cpu_present(), but we > need to be able to call sysfs_update_groups() when the state of the > .is_visible() changes. > > Given the comment in sysfs_update_groups() about "if an error occurs", > rather than making this part of common_cpu_attr_groups, would it be > better that it's part of its own set of groups, thus limiting the > damage from a possible error? I suspect, however, that any error at > that point means that the system is rather fatally wounded. > > This is what I have so far to implement your idea, less the necessary > sysfs_update_groups() call when we need to change the visibility of > the attributes. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
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