| From: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Álvaro Herrera <alvherre(at)kurilemu(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Salvatore Dipietro <dipietro(dot)salvatore(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org, Salvatore Dipietro <dipiets(at)amazon(dot)com>, blakgeof(at)amazon(dot)com |
| Subject: | Re: Remove Instruction Synchronization Barrier in spin_delay() for ARM64 architecture |
| Date: | 2025-08-15 17:57:52 |
| Message-ID: | aJ91IK8h3x8B-9WA@nathan |
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| Lists: | pgsql-hackers |
On Fri, Aug 15, 2025 at 01:39:52PM -0400, Andres Freund wrote:
> On 2025-08-14 11:29:08 +0200, Álvaro Herrera wrote:
>> However, changing that spinlock to an lwlock doesn't look easy, because of
>> the way each pgss entry is created as a dynahash entry, and then deallocated
>> from there. With spinlocks we can just reinit the spinlock each time, but
>> that doesn't work with lwlocks. We have no easy way to associate then
>> disassociate each entry from a specific lwlock.
>
> I'm not following? The lwlock can just be inside the struct, just like the
> spinlock is? "Association" is just LWLockInitialize() and deassociation is not
> needed.
Indeed. I rebased an old patch that I had lying around to demonstrate. If
my past testing [0] is to be trusted, this actually hurts performance,
unfortunately.
[0] https://postgr.es/m/Zs4hJ6-Fg8DMgU_P@nathan
--
nathan
| Attachment | Content-Type | Size |
|---|---|---|
| v1-0001-replace-p_s_s-entry-spinlocks-with-lwlocks.patch | text/plain | 3.2 KB |
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