Date: Fri, 10 Jan 2025 10:51:40 -0600
From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, dipiets@amazon.com
Subject: Re: use a non-locking initial test in TAS_SPIN on AArch64
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On Wed, Jan 08, 2025 at 04:38:02PM -0600, Nathan Bossart wrote:
> On Wed, Jan 08, 2025 at 05:25:24PM -0500, Andres Freund wrote:
>> I wonder if you're hitting an extreme case of binary-layout related effects?
>> I've never seen them at this magnitude though.  I'd suggest using either lld
>> or mold as linker and comparing the numbers for a few
>> -Wl,--shuffle-sections=$seed seed values.
> 
> Will do.

Actually, I think I may have just had back luck and/or not warmed things up
enough.  I just re-ran the test a few dozen times, carefully ensuring the
data was in the cache and periodically alternating between the binary with
the patch applied and the one without it.  The results converged to within
1-2% of each other, with the patched version even winning about half the
time.  The averages across all the runs showed a ~0.4% regression, which I
suspect is well within the noise range.

-- 
nathan