Re: [RFC][PATCH] O(1) Entitlement Based Scheduler

[Pavel Machek <pavel@ucw.cz>]

Hi!

> CPU usage rate caps
> -------------------
> 
> A task's CPU usage rate cap imposes a soft (or hard) upper limit on the rate at
> which it can use CPU resources and can be set/read via the files 
> 
> /proc/<pid>/cpu_rate_cap 
> /proc/<tgid>/task/<pid>/cpu_rate_cap  
> 
> Usage rate caps are expressed as rational numbers (e.g. "1 / 2") and hard caps 
> are signified by a "!" suffix.  The rational number indicates the proportion 
> of a single CPU's capacity that the task may use. The value of the number must 
> be in the range 0.0 to 1.0 inclusive for soft caps. For hard caps there is an 
> additional restriction that a value of 0.0 is not permitted.  Tasks with a 
> soft cap of 0.0 become true background tasks and only get to run when no other 
> tasks are active.

Why not use something like percent, parts per milion or whatever?

> When hard capped tasks exceed their cap they are removed from the run queues 
> and placed in a "sinbin" for a short while until their usage rate decays to
> within limits.

How do you solve this one?

I want to kill your system.

I launch task A, "semaphore grabber", that does filesystem
operations. Those need semaphores. I run it as "true background".

I wait for A to grab some lock, then I run B, which is while(1);

A holds lock that can not be unlocked, and your system is dead.

This may happen randomly, even without me on your system.
								Pavel
-- 
When do you have a heart between your knees?
[Johanka's followup: and *two* hearts?]