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Mon, 10 Feb 2025 03:01:24 -0800 (PST) Date: Mon, 10 Feb 2025 12:01:23 +0100 From: Andrew Jones To: Anup Patel Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, paul.walmsley@sifive.com, palmer@dabbelt.com, charlie@rivosinc.com, jesse@rivosinc.com Subject: Re: [PATCH 0/9] riscv: Unaligned access speed probing fixes and skipping Message-ID: <20250210-c79541eaea0d2d922f019384@orel> References: <20250207161939.46139-11-ajones@ventanamicro.com> <20250210-d575562e04d84ca570e26f5d@orel> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Feb 10, 2025 at 03:28:13PM +0530, Anup Patel wrote: > On Mon, Feb 10, 2025 at 2:56 PM Andrew Jones wrote: > > > > On Sat, Feb 08, 2025 at 01:29:42PM +0530, Anup Patel wrote: > > > On Fri, Feb 7, 2025 at 9:49 PM Andrew Jones wrote: > > > > > > > > The first six patches of this series are fixes and cleanups of the > > > > unaligned access speed probing code. The next two patches introduce > > > > support to skip probing by matching vendor/arch/imp ids and checking a > > > > table for the access speed type. The last patch applies the new skip > > > > support to Ventana harts. > > > > > > Alternatively, we can also skip probing misaligned access when Zicclsm > > > extension is present in the ISA string. The Zicclsm extension is defined > > > as part of the ratified RVA23 profile. > > > > The definition of Zicclsm doesn't explicitly state that misaligned word > > accesses will be faster than byte accesses to the same addresses. There's > > also this spec issue[1] which appears to state that Zicclsm cannot be used > > to infer fast misaligned accesses. > > > > But, like Charlie suggests, maybe we should advocate the creation of an > > extension (or "named feature") which allows specifically advertising that > > misaligned accesses are fast. > > > > [1] https://github.com/riscv/riscv-isa-manual/issues/1611 > > I am not sure when such an extension would show up so for now > skipping unaligned tests based on implementation ID seems > reasonable. > > Also, it seems this series is totally skipping the existing boot-time > print for fast unaligned access. Please try to keep the boot-time > print in some form. Sure. We have hwprobe, but now that people are likely used to seeing it in dmesg, then we should probably keep something there. Thanks, drew