| From: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>, Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Lockless queue of waiters in LWLock |
| Date: | 2022-11-05 09:05:43 |
| Message-ID: | CAPpHfduRgLH9a+U=6pYR7KawCosNO764ojCZkSajdFAbbE8sgQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi, Andres!
On Fri, Nov 4, 2022 at 10:07 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> The use of cmpxchg vs lock inc/lock add/xadd is one of the major reasons why
> lwlocks are slower than a spinlock (but obviously are better under contention
> nonetheless).
>
>
> I have a benchmark program that starts a thread for each physical core and
> just increments a counter on an atomic value.
Thank you for this insight! I didn't know xadd is much cheaper than
cmpxchg unless there are retries. I also wonder how cmpxchg becomes
faster with higher concurrency.
------
Regards,
Alexander Korotkov
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