Re: [RFC PATCH 0/3] Implement getcpu_cache system call

[Josh Triplett]

On Mon, Jan 11, 2016 at 10:38:28PM +0000, Seymour, Shane M wrote:
> I have some concerns and suggestions for you about this.
> 
> What's to stop someone in user space from requesting an arbitrarily large number of CPU # cache locations that the kernel needs to allocate memory to track and each time the task migrates to a new CPU it needs to update them all? Could you use it to dramatically slow down a system/task switching? Should there be a ulimit type value or a sysctl setting to limit the number that you're allowed to register per-task?

The documented behavior of the syscall allows only one location per
thread, so the kernel can track that one and only address rather easily
in the task_struct.  Allowing dynamic allocation definitely doesn't seem
like a good idea.

- Josh Triplett