[PATCH v2] rwlock: Fix explicit hand-over.

[Waiman Long]

On 03/25/2017 07:01 PM, Torvald Riegel wrote:
> On Sat, 2017-03-25 at 21:17 +0100, Florian Weimer wrote:
>> * Torvald Riegel:
>>
>>> +  bool registered_while_in_write_phase = false;
>>>    if (__glibc_likely ((r & PTHREAD_RWLOCK_WRPHASE) == 0))
>>>      return 0;
>>> +  else
>>> +    registered_while_in_write_phase = true;
>> Sorry, this doesn't look quite right.  Isn't
>> registered_while_in_write_phase always true?
> Attached is a v2 patch.  It's the same logic, but bigger.  Most of this
> increase is due to reformatting, but I also adapted some of the
> comments.
> I get two failures, but I guess these are either due to the bad internet
> connectivity I currently have, or something at the resolver.
> FAIL: resolv/mtrace-tst-leaks
> FAIL: resolv/tst-leaks
>
>
I have verified that the v2 patch did fix the hang that I saw with my
microbenchmark. I also observed an increase in performance in the new
rwlock code compared with the old one before the major rewrite. On a
4-socket 40-core 80-thread system, 80 parallel locking threads had an
average per-thread throughput of 32,584 ops/s. The old rwlock code had a
throughput of 13,411 only. So there is a more than 1.4X increase in
performance.

Tested-by: Waiman Long <longman@redhat.com>

Cheers,
Longman