Re: [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation

Waiman Long
2016-06-15T19:31:51Z

On 06/15/2016 01:43 PM, Peter Zijlstra wrote:
> On Tue, Jun 14, 2016 at 06:48:08PM -0400, Waiman Long wrote:
>> even the reduced maximum of about 16k (32-bit) or 1G (64-bit) should
>> be more than enough for the foreseeable future.
> So what happens if I manage to create 16k+ threads on my 32bit kernel
> and get them all to do mmap() or so at the same time.
>
> That doesn't seem too far fetched.
>
> Then again, with double that (the current limit) that doesn't seem
> impossible either.

To hit the limit, we need to have all the threads calling down_write()
at exactly the same instance in time which, I think, is pretty hard to
do. Also, I don't believe you will ever see a 16k-cpu massive SMP system
running on 32-bit kernel. I can imagine such a system running on 64-bit
kernel, but certainly not 32-bit.

Cheers,
Longman