From: Jeff Law <jeffreyalaw@gmail.com>
To: "Adhemerval Zanella Netto" <adhemerval.zanella@linaro.org>,
"Christoph Müllner" <christoph.muellner@vrull.eu>,
"Xi Ruoyao" <xry111@xry111.site>
Cc: libc-alpha@sourceware.org, Palmer Dabbelt <palmer@dabbelt.com>,
Darius Rad <darius@bluespec.com>,
Andrew Waterman <andrew@sifive.com>, DJ Delorie <dj@redhat.com>,
Vineet Gupta <vineetg@rivosinc.com>,
Kito Cheng <kito.cheng@sifive.com>,
Philipp Tomsich <philipp.tomsich@vrull.eu>,
Heiko Stuebner <heiko.stuebner@vrull.eu>
Subject: Re: [RFC PATCH 16/19] riscv: Add accelerated strcmp routines
Date: Fri, 31 Mar 2023 08:30:59 -0600 [thread overview]
Message-ID: <2400cf77-8258-1bdb-a3a0-3c0e65949b01@gmail.com> (raw)
In-Reply-To: <c83ac3ee-e466-6a6b-0ebf-ecba1f9e7f3d@linaro.org>
On 3/31/23 06:31, Adhemerval Zanella Netto wrote:
>> Jeff
>
> Is this implementation really better than new generic one [1]? With a target
> with zbb support, the generic word comparison should use orc.b instruction [2].
> And the final comparison, once with the last word or the mismatch word is found,
> should use clz/ctz instruction [3] (result also in branchless code, albeit
> I have not check if better than the snippet this implementation uses).
I haven't done any comparisons against the updated generic bits. I
nearly suggested to Christoph to do that evaluation, but when I wandered
around sysdeps I saw that we still had multiple custom strcmp
implementations and set that suggestion aside.
>
> The generic implementation also has the advantage of use word instruction
> on unaligned case, where this implementation does a naive byte per byte
> check.
Yea, but in my digging this just didn't happen terribly often. I don't
think there's a lot of value there. Along the same lines, my
investigation didn't show any significant value to realign cases and I
nearly suggested dropping them to avoid the branch in the hot path, but
I wasn't confident enough in the breadth of my investigations to push it.
>
> So maybe a better option would to optimize further the generic implementation.
> One option might be to parametrize the final_cmp so you can use the branchless
> trick (if it indeed is better than generic code). Another option that the
> generic implementation does not explore is manual loop unrolling, as done by
> multiple assembly implementations.
I could certainly support that. I was on the fence about pushing to use
the generic bits, a little nudge could easily push me to that side.
jeff
next prev parent reply other threads:[~2023-03-31 14:31 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 0:15 [RFC PATCH 00/19] riscv: ifunc support with optimized mem*/str*/cpu_relax routines Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 01/19] Inhibit early libcalls before ifunc support is ready Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 02/19] riscv: LEAF: Use C_LABEL() to construct the asm name for a C symbol Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 03/19] riscv: Add ENTRY_ALIGN() macro Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 04/19] riscv: Add hart feature run-time detection framework Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 05/19] riscv: Introduction of ISA extensions Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 06/19] riscv: Adding ISA string parser for environment variables Christoph Muellner
2023-02-07 6:20 ` David Abdurachmanov
2023-02-07 0:16 ` [RFC PATCH 07/19] riscv: hart-features: Add fast_unaligned property Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 08/19] riscv: Add (empty) ifunc framework Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 09/19] riscv: Add ifunc support for memset Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 10/19] riscv: Add accelerated memset routines for RV64 Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 11/19] riscv: Add ifunc support for memcpy/memmove Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 12/19] riscv: Add accelerated memcpy/memmove routines for RV64 Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 13/19] riscv: Add ifunc support for strlen Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 14/19] riscv: Add accelerated strlen routine Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 15/19] riscv: Add ifunc support for strcmp Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 16/19] riscv: Add accelerated strcmp routines Christoph Muellner
2023-02-07 11:57 ` Xi Ruoyao
2023-02-07 14:15 ` Christoph Müllner
2023-03-31 5:06 ` Jeff Law
2023-03-31 12:31 ` Adhemerval Zanella Netto
2023-03-31 14:30 ` Jeff Law [this message]
2023-03-31 14:48 ` Adhemerval Zanella Netto
2023-03-31 17:19 ` Palmer Dabbelt
2023-03-31 14:32 ` Jeff Law
2023-02-07 0:16 ` [RFC PATCH 17/19] riscv: Add ifunc support for strncmp Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 18/19] riscv: Add an optimized strncmp routine Christoph Muellner
2023-02-07 1:19 ` Noah Goldstein
2023-02-08 15:13 ` Philipp Tomsich
2023-02-08 17:55 ` Palmer Dabbelt
2023-02-08 19:48 ` Adhemerval Zanella Netto
2023-02-08 18:04 ` Noah Goldstein
2023-02-07 0:16 ` [RFC PATCH 19/19] riscv: Add __riscv_cpu_relax() to allow yielding in busy loops Christoph Muellner
2023-02-07 0:23 ` Andrew Waterman
2023-02-07 0:29 ` Christoph Müllner
2023-02-07 2:59 ` [RFC PATCH 00/19] riscv: ifunc support with optimized mem*/str*/cpu_relax routines Kito Cheng
2023-02-07 16:40 ` Adhemerval Zanella Netto
2023-02-07 17:16 ` DJ Delorie
2023-02-07 19:32 ` Philipp Tomsich
2023-02-07 21:14 ` DJ Delorie
2023-02-08 11:26 ` Christoph Müllner
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