Re: [RFC PATCH 0/3] Implement getcpu_cache system call
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From: Josh Triplett <josh@joshtriplett.org>
Date: 2016-01-11 23:03:19
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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