From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: John Naylor <johncnaylorls@gmail.com>
Cc: Ants Aasma <ants@cybertec.at>
Cc: pgsql-hackers@postgresql.org
Subject: Re: add AVX2 support to simd.h
Date: Wed, 27 Mar 2024 13:57:16 -0500
Message-ID: <20240327185716.GA4188857@nathanxps13> (raw)
In-Reply-To: <3206056.1711504137@sss.pgh.pa.us>
References: <CANWCAZYfUv3iN2Vx--tmQP9WU6xwfU8d=gA7LoFXOYP9-wo8Hg@mail.gmail.com>
<20240321170944.GA1767527@nathanxps13>
<CANWCAZb7TGEk6ib12Rr6pbGMy9pqofT0dS=8Dkm+=MwJQZAEww@mail.gmail.com>
<20240325152121.GB2662364@nathanxps13>
<20240325213754.GA3094030@nathanxps13>
<20240326190904.GA3700674@nathanxps13>
<3189995.1711495704@sss.pgh.pa.us>
<20240326235554.GA3766883@nathanxps13>
<20240327013616.GA3940109@nathanxps13>
<3206056.1711504137@sss.pgh.pa.us>
On Tue, Mar 26, 2024 at 09:48:57PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> I just did the minimal fix for now, i.e., I moved the new label into the
>> SIMD section of the function. I think it would be better stylistically to
>> move the one-by-one logic to an inline helper function, but I didn't do
>> that just in case it might negatively impact performance. I'll look into
>> this and will follow up with another patch if it looks good.
>
> Sounds like a plan.
Here's what I had in mind. My usual benchmark seems to indicate that this
shouldn't impact performance.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.comAttachments:v1-0001-improve-style-of-pg_lfind32.patch (text/x-diff, 2.8K) download
From c3f163753246c5ec82dd8c5dba70232cbeebbf2a Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 27 Mar 2024 13:50:17 -0500
Subject: [PATCH v1 1/1] improve style of pg_lfind32()
---
src/include/port/pg_lfind.h | 58 +++++++++++++++----------------------
1 file changed, 24 insertions(+), 34 deletions(-)
diff --git a/src/include/port/pg_lfind.h b/src/include/port/pg_lfind.hindex 33e8471b03..5b76cc8937 100644--- a/src/include/port/pg_lfind.h+++ b/src/include/port/pg_lfind.h@@ -80,6 +80,24 @@ pg_lfind8_le(uint8 key, uint8 *base, uint32 nelem)
return false;
}
+/*+ * pg_lfind32_one_by_one_helper+ *+ * Searches the array of integers one-by-one. The caller is responsible for+ * ensuring that there are at least "nelem" integers in the array.+ */+static inline bool+pg_lfind32_one_by_one_helper(uint32 key, uint32 *base, uint32 nelem)+{+ for (int i = 0; i < nelem; i++)+ {+ if (key == base[i])+ return true;+ }++ return false;+}+
#ifndef USE_NO_SIMD
/*
* pg_lfind32_simd_helper
@@ -134,9 +152,8 @@ pg_lfind32_simd_helper(const Vector32 keys, uint32 *base)
static inline bool
pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
{
- uint32 i = 0;-
#ifndef USE_NO_SIMD
+ uint32 i = 0;
/*
* For better instruction-level parallelism, each loop iteration operates
@@ -150,25 +167,15 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
const uint32 tail_idx = nelem & ~(nelem_per_iteration - 1);
#if defined(USE_ASSERT_CHECKING)
- bool assert_result = false;-- /* pre-compute the result for assert checking */- for (int j = 0; j < nelem; j++)- {- if (key == base[j])- {- assert_result = true;- break;- }- }+ bool assert_result = pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
/*
- * If there aren't enough elements for the SIMD code, jump to the standard+ * If there aren't enough elements for the SIMD code, use the standard
* one-by-one linear search code.
*/
if (nelem < nelem_per_iteration)
- goto one_by_one;+ return pg_lfind32_one_by_one_helper(key, base, nelem);
/*
* Process as many elements as possible with a block of 4 registers.
@@ -193,27 +200,10 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
*/
Assert(assert_result == pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]));
return pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]);
--one_by_one:--#endif /* ! USE_NO_SIMD */-+#else
/* Process the elements one at a time. */
- for (; i < nelem; i++)- {- if (key == base[i])- {-#ifndef USE_NO_SIMD- Assert(assert_result == true);+ return pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
- return true;- }- }--#ifndef USE_NO_SIMD- Assert(assert_result == false);-#endif- return false;
}
#endif /* PG_LFIND_H */
--
2.25.1
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, tgl@sss.pgh.pa.us, johncnaylorls@gmail.com, ants@cybertec.at
Subject: Re: add AVX2 support to simd.h
In-Reply-To: <20240327185716.GA4188857@nathanxps13>
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