* Noah Meyerhans:

> On Sun, Apr 12, 2020 at 12:18:35PM +0200, Aurelien Jarno wrote:
>> > Significant performance impact has also been observed in less contrived
>> > cases (MariaDB and Postgres), but I don't have a repro to share.
>> But indeed what counts is number on real workloads. It would be nice to
>> get numbers when those software are run against a rebuilt glibc. As
>> those software are using a lot of atomics directly, it would be also
>> interesting to have numbers with those software also rebuilt to use
>> those new instructions.
> Agreed.  I don't have specific examples of real world impact at the
> moment.  AIUI, the most significant impact comes in the usage of atomics
> in pthread_mutex_lock().  When there are multiple threads contending for
> a lock, one thread will (approximately) always obtain the lock, while
> the others will starve.  With atomics support in place, the probability
> of obtaining the lock is roughly evenly distributed among all the
> threads.  So any workload in which multiple threads may contend for a
> lock should be a candidate to demonstrate this problem in the real
> world.

Does this behavior affect just one implementation with LSE, or also
implementations without LSE?

If the latter, we might need a different mutex implementation for
AArch64. 8-(

Reply via email to