On Wed, 21 Dec 2005, Ravikiran G Thirumalai wrote:
> Following patch avoids taking the global tasklist_lock when possible,
> if a process is single threaded during getrusage(). Any avoidance of
> tasklist_lock is good for NUMA boxes (and possibly for large SMPs). We found
> that this optimization reduces the runtime of a certain scientific application
> by half on a 16 cpu NUMA box.
>
> This optimization is similar to the sys_times tasklist_lock optimization.
The optimization of sys_times is only possible because the "current"
task is running and therefore guarantees that the thread will not be
exiting.
getrusage and k_getrusage can be called onother tasks than the currently
executing task and in those cases better take the tasklist lock because
the task may exit while getrusage runs.
See wait_noreap_copyout() in kernel/exit.c and
arch/mips/kernel/{sysirix,irixsig}.c for uses of getrusage where the
struct task_struct * != current.
Maybe you can deal with these and insure that getrusage is always called
for the current process? In that case the struct task_struct * parameter
needs to be dropped from getrusage and k_getrusage.
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