rusage breakdown and cpu limits.

[John Baldwin]

On Tuesday 29 May 2007 02:01:36 pm Jeff Roberson wrote:
> I'm working with Attilio to break down rusage further to be per-thread in 
> places where it is protected by the global scheduler lock.  To support 
> this, I am interested in moving the rlimit cpulimit check into userret(), 
> or perhaps ast().  Is there any reason why we need to check this on every 
> context switch?  Any objections to moving it?  Eventually it will require 
> a different lock from the one we obtain to call mi_switch().

I think using a per-process spin lock (or a pool of spin locks) would be a 
good first step.  I wouldn't do anything more complicated unless the simple 
approach doesn't work.  The only reason to not move the check into userret() 
would be if one is worried about threads chewing up CPU time while they are 
in the kernel w/o bouncing out to userland.  Also, it matters which one 
happens more often (userret() vs mi_switch()).  If on average threads perform 
multiple system calls during a single time slice (no idea if this is true or 
not), then moving the check to userret() would actually hurt performance.

-- 
John Baldwin