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help / color / mirror / Atom feedFrom: Nathan Bossart <[email protected]>
To: David Rowley <[email protected]>
Cc: Amonson, Paul D <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Shankaran, Akash <[email protected]>
Cc: Noah Misch <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Popcount optimization using AVX512
Date: Mon, 18 Mar 2024 16:29:19 -0500
Message-ID: <20240318212919.GA684016@nathanxps13> (raw)
In-Reply-To: <CAApHDvojPyh6dLKooqjXSZE=0Ed590Lq1BxF7WQ9knSggyuJEA@mail.gmail.com>
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<20240318152902.GA2850@nathanxps13>
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<20240318162018.GA204772@nathanxps13>
<20240318173004.GA361138@nathanxps13>
<CAApHDvqyMNGVgwpaOPtENdq5uEMR=vSkRJEgG1S+X7Vtk1-EnA@mail.gmail.com>
<20240318210810.GA582529@nathanxps13>
<CAApHDvojPyh6dLKooqjXSZE=0Ed590Lq1BxF7WQ9knSggyuJEA@mail.gmail.com>
On Tue, Mar 19, 2024 at 10:27:58AM +1300, David Rowley wrote:
> On Tue, 19 Mar 2024 at 10:08, Nathan Bossart <[email protected]> wrote:
>> On Tue, Mar 19, 2024 at 10:02:18AM +1300, David Rowley wrote:
>> > The only thing I'd question in the patch is in pg_popcount_fast(). It
>> > looks like you've opted to not do the 32-bit processing on 32-bit
>> > machines. I think that's likely still worth coding in a similar way to
>> > how pg_popcount_slow() works. i.e. use "#if SIZEOF_VOID_P >= 8".
>> > Probably one day we'll remove that code, but it seems strange to have
>> > pg_popcount_slow() do it and not pg_popcount_fast().
>>
>> The only reason I left it out was because I couldn't convince myself that
>> it wasn't dead code, given we assume that popcntq is available in
>> pg_popcount64_fast() today. But I don't see any harm in adding that just
>> in case.
>
> It's probably more of a case of using native instructions rather than
> ones that might be implemented only via microcode. For the record, I
> don't know if that would be the case for popcntq on x86 32-bit and I
> don't have the hardware to test it. It just seems less risky just to
> do it.
Agreed. Will send an updated patch shortly.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
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To: [email protected]
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Subject: Re: Popcount optimization using AVX512
In-Reply-To: <20240318212919.GA684016@nathanxps13>
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