Re: futex testsuite suggestion...

From: Darren Hart
Date: Sun Nov 23 2014 - 00:24:36 EST

On Mon, Oct 27, 2014 at 04:31:16PM -0400, David Miller wrote:
> From: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
> Date: Mon, 27 Oct 2014 13:29:14 -0700
> > On 10/27/14 12:56, David Miller wrote:
> >> I'd like to suggest that you add a test that triggers transparent
> >> hugepages, because if an architecture doesn't implement
> >> __get_user_pages_fast() such futexes cause a machine to hang.
> >>
> >> I hacked up something simple that took the existing performance
> >> test and made it operate in a register allocated using memalign().
> >>
> >> I would suggest doing a memalign(HUGEPAGE_SIZE, HUGEPAGE_SIZE) then
> >> iterating running a futex test within each normal page within that
> >> hugepage.
> >
> > Do you want this option for the performance tests, or would a less
> > intensive functional test be sufficient?
> I think a functional test is sufficient.

Hi David,

>From your suggestion I put together a simple transparent hugepage functional
test. See the "thp" branch, functional/futex_wait_thp.c.

I'd like your thoughts on if this functions as desired. Is the simple single
threaded timeout sufficient, or would you prefer to see a waiter/waker pair of
threads for each iteration?

Some TODOs still:

I wasn't sure if there was a way to test for hugepagesize and my quick search
didn't reveal anything (other than /proc/meminfo).

Check at runtime if the test is getting a huge page, otherwise it just reports
success, but used several regular pages instead.

Darren Hart
Intel Open Source Technology Center
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