From: Sunil Pandey <skpgkp2@gmail.com>
To: Arjan van de Ven <arjan@linux.intel.com>,
Libc-stable Mailing List <libc-stable@sourceware.org>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
Noah Goldstein <goldstein.w.n@gmail.com>,
Florian Weimer <fweimer@redhat.com>,
Andreas Schwab <schwab@linux-m68k.org>,
GNU C Library <libc-alpha@sourceware.org>,
"Paul A . Clarke" <pc@us.ibm.com>
Subject: Re: [PATCH v6 1/4] Add LLL_MUTEX_READ_LOCK [BZ #28537]
Date: Sun, 11 Sep 2022 13:19:15 -0700 [thread overview]
Message-ID: <CAMAf5_fsUuYbUdiD2KmAV-4RH6QV=k8swJzkOL02awZXbO1NDg@mail.gmail.com> (raw)
In-Reply-To: <924a80cd-202c-99e9-a2d9-1aeda2235b83@linux.intel.com>
On Wed, Nov 17, 2021 at 5:17 PM Arjan van de Ven via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On 11/17/2021 4:31 PM, H.J. Lu wrote:
> >> Yes, but the loop will be able to run `max_cnt` iterations much faster now.
> >> Just wondering if the value needs to be re-tuned. Not that is necessarily needs
> >> to be.
> > Maybe if we can find some data to show for.
> >
>
> wondering when this was last tuned.. I assume todays CPUs and CPUs from, say, 5 or 10 years ago
> have an order of magnitude different performance in this regard....
> if there wasn't a need to retune during that, maybe this value is so robust that it doesn't need
> retuning.
>
> or maybe it's time to retune this in general sometime soon after this patch goes in ;)
I would like to backport this patch to release branch 2.33 and 2.34
Any comments/suggestions or objections on this.
commit d672a98a1af106bd68deb15576710cd61363f7a6
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Tue Nov 2 18:33:07 2021 -0700
Add LLL_MUTEX_READ_LOCK [BZ #28537]
CAS instruction is expensive. From the x86 CPU's point of view, getting
a cache line for writing is more expensive than reading. See Appendix
A.2 Spinlock in:
https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/xeon-lock-scaling-analysis-paper.pdf
next prev parent reply other threads:[~2022-09-11 20:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 16:24 [PATCH v6 0/4] Optimize CAS " H.J. Lu
2021-11-11 16:24 ` [PATCH v6 1/4] Add LLL_MUTEX_READ_LOCK " H.J. Lu
2021-11-12 17:23 ` Szabolcs Nagy
2021-11-17 2:24 ` Noah Goldstein
2021-11-17 23:54 ` H.J. Lu
2021-11-18 0:03 ` Noah Goldstein
2021-11-18 0:31 ` H.J. Lu
2021-11-18 1:16 ` Arjan van de Ven
2022-09-11 20:19 ` Sunil Pandey [this message]
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` [PATCH v6 2/4] Avoid extra load with CAS in __pthread_mutex_lock_full " H.J. Lu
2021-11-12 16:31 ` Szabolcs Nagy
2021-11-12 18:50 ` Andreas Schwab
2022-09-11 20:16 ` Sunil Pandey
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` [PATCH v6 3/4] Reduce CAS in malloc spinlocks H.J. Lu
2023-02-23 5:48 ` DJ Delorie
2021-11-11 16:24 ` [PATCH v6 4/4] Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537] H.J. Lu
2021-11-12 16:32 ` Szabolcs Nagy
2021-11-12 18:51 ` Andreas Schwab
2022-09-11 20:12 ` Sunil Pandey
2022-09-11 20:15 ` Arjan van de Ven
2022-09-11 21:26 ` Florian Weimer
2022-09-29 0:09 ` Noah Goldstein
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