On 14-Sep 13:10, Peter Zijlstra wrote: > On Thu, Sep 06, 2018 at 03:40:53PM +0100, Patrick Bellasi wrote: > > 1) _I think_ we don't want to depend on capable(CAP_SYS_NICE) but > > instead on capable(CAP_SYS_ADMIN) > > > > Does that make sense ? > > Neither of them really makes sense to me. > > The max clamp makes a task 'consume' less and you should always be able > to reduce yourself. > > The min clamp doesn't avoid while(1); and is therefore also not a > problem. > > So I think setting clamps on a task should not be subject to additional > capabilities. > > Now, of course, there is a problem of clamp resources, which are > limited. Consuming those _is_ a problem.
Right, that problem could be solved if we convince ourself that the quantization approach proposed in: [PATCH v4 15/16] sched/core: uclamp: add clamp group discretization support https://lore.kernel.org/lkml/20180828135324.21976-16-patrick.bell...@arm.com/ could make sense and specifically, the other limitation it imposes (i.e. the quantizaiton) is within reasonable rounding control errors/ > I think the problem here is that the two are conflated in the very same > interface. > > Would it make sense to move the available clamp values out to some sysfs > interface like thing and guard that with a capability, while keeping the > task interface unprivilidged? You mean something like: $ cat /proc/sys/kernel/sched_uclamp_min_utils 0 10 20 ... 100 to notify users about the set of clamp values which are available ? > Another thing that has me 'worried' about this interface is the direct > tie to CPU capacity (not that I have a better suggestion). But it does > raise the point of how userspace is going to discover the relevant > values of the platform. This point worries me too, and that's what I think is addressed in a sane way in: [PATCH v4 13/16] sched/core: uclamp: use percentage clamp values https://lore.kernel.org/lkml/20180828135324.21976-14-patrick.bell...@arm.com/ IMHO percentages are a reasonably safe and generic API to expose to user-space. Don't you think this should address your concern above ? -- #include <best/regards.h> Patrick Bellasi
