Re: [CFT][RFC] HT scheduler

Nick Piggin
2003-12-11T15:31:51Z

William Lee Irwin III wrote:

>William Lee Irwin III wrote:
>
>>>It will get contention anyway if they're all pounding on the same futex.
>>>OTOH, if they're all threads in the same process, they can hit other
>>>problems. I'll try to find out more about hackbench.
>>>
>
>
>On Fri, Dec 12, 2003 at 12:30:07AM +1100, Nick Piggin wrote:
>
>>Oh, sorry I was talking about volanomark. hackbench AFAIK doesn't use
>>futexes at all, just pipes, and is not threaded at all, so it looks like
>>a different problem to the volanomark one.
>>hackbench runs into trouble at large numbers of tasks too though.
>>
>
>Volano is all one process address space so it could be ->page_table_lock;
>any chance you could find which spin_lock() call the pounded chunk of the
>lock section jumps back to?
>
>

OK its in futex_wait, up_read(&current->mm->mmap_sem) right after
out_release_sem (line 517).

So you get half points. Looks like its waiting on the bus rather than
spinning on a lock. Or am I'm wrong?