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R. Silva" , Erick Archer , Joel Granados , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Subject: Re: [PATCH 1/1] RISC-V: Add parameter to unaligned access speed Message-ID: References: <20240805173816.3722002-1-jesse@rivosinc.com> Precedence: bulk X-Mailing-List: linux-doc@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, Aug 05, 2024 at 11:38:23AM -0700, Evan Green wrote: > On Mon, Aug 5, 2024 at 10:38 AM Jesse Taube wrote: > > > > Add a kernel parameter to the unaligned access speed. This allows > > skiping of the speed tests for unaligned accesses, which often is very > > slow. > > > > Signed-off-by: Jesse Taube > > How come this is a command line parameter rather than a Kconfig > option? I could be wrong, so I'll lay out my rationale and people can > pick it apart if I've got a bad assumption. > > I think of commandline parameters as (mostly) something end users > twiddle with, versus kconfig options as something system builders set > up. I'd largely expect end users not to notice two ticks at boot time. > I'd expect its system builders and fleet managers, who know their > hardware and build their kernels optimized for it, are the ones who > would want to shave off this time and go straight to the known answer. > Anecdotally, at ChromeOS we had a strong preference for Kconfig > options, as they were easier to compose and maintain than a loose pile > of commandline arguments. > > The commit text doesn't go into the rationale, intended audience, or > expected usage, so maybe my guesses miss the mark on what you're > thinking. > -Evan There was a brief discussion about this on Jesse's series about vector unaligned support [1]. The original idea was to use Zicclsm to allow people to set the unaligned access speed on pre-compiled distro kernels. However Zicclsm isn't useful so the alternative route was to use a kernel arg. There is already support for a Kconfig, the kernel arg is just another option for users. 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Silva" , Erick Archer , Joel Granados , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Subject: Re: [PATCH 1/1] RISC-V: Add parameter to unaligned access speed Message-ID: References: <20240805173816.3722002-1-jesse@rivosinc.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240805_114817_417237_134517BB X-CRM114-Status: GOOD ( 21.57 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org T24gTW9uLCBBdWcgMDUsIDIwMjQgYXQgMTE6Mzg6MjNBTSAtMDcwMCwgRXZhbiBHcmVlbiB3cm90 ZToKPiBPbiBNb24sIEF1ZyA1LCAyMDI0IGF0IDEwOjM44oCvQU0gSmVzc2UgVGF1YmUgPGplc3Nl QHJpdm9zaW5jLmNvbT4gd3JvdGU6Cj4gPgo+ID4gQWRkIGEga2VybmVsIHBhcmFtZXRlciB0byB0 aGUgdW5hbGlnbmVkIGFjY2VzcyBzcGVlZC4gVGhpcyBhbGxvd3MKPiA+IHNraXBpbmcgb2YgdGhl IHNwZWVkIHRlc3RzIGZvciB1bmFsaWduZWQgYWNjZXNzZXMsIHdoaWNoIG9mdGVuIGlzIHZlcnkK PiA+IHNsb3cuCj4gPgo+ID4gU2lnbmVkLW9mZi1ieTogSmVzc2UgVGF1YmUgPGplc3NlQHJpdm9z aW5jLmNvbT4KPiAKPiBIb3cgY29tZSB0aGlzIGlzIGEgY29tbWFuZCBsaW5lIHBhcmFtZXRlciBy YXRoZXIgdGhhbiBhIEtjb25maWcKPiBvcHRpb24/IEkgY291bGQgYmUgd3JvbmcsIHNvIEknbGwg bGF5IG91dCBteSByYXRpb25hbGUgYW5kIHBlb3BsZSBjYW4KPiBwaWNrIGl0IGFwYXJ0IGlmIEkn dmUgZ290IGEgYmFkIGFzc3VtcHRpb24uCj4gCj4gSSB0aGluayBvZiBjb21tYW5kbGluZSBwYXJh bWV0ZXJzIGFzIChtb3N0bHkpIHNvbWV0aGluZyBlbmQgdXNlcnMKPiB0d2lkZGxlIHdpdGgsIHZl cnN1cyBrY29uZmlnIG9wdGlvbnMgYXMgc29tZXRoaW5nIHN5c3RlbSBidWlsZGVycyBzZXQKPiB1 cC4gSSdkIGxhcmdlbHkgZXhwZWN0IGVuZCB1c2VycyBub3QgdG8gbm90aWNlIHR3byB0aWNrcyBh dCBib290IHRpbWUuCj4gSSdkIGV4cGVjdCBpdHMgc3lzdGVtIGJ1aWxkZXJzIGFuZCBmbGVldCBt YW5hZ2Vycywgd2hvIGtub3cgdGhlaXIKPiBoYXJkd2FyZSBhbmQgYnVpbGQgdGhlaXIga2VybmVs cyBvcHRpbWl6ZWQgZm9yIGl0LCBhcmUgdGhlIG9uZXMgd2hvCj4gd291bGQgd2FudCB0byBzaGF2 ZSBvZmYgdGhpcyB0aW1lIGFuZCBnbyBzdHJhaWdodCB0byB0aGUga25vd24gYW5zd2VyLgo+IEFu ZWNkb3RhbGx5LCBhdCBDaHJvbWVPUyB3ZSBoYWQgYSBzdHJvbmcgcHJlZmVyZW5jZSBmb3IgS2Nv bmZpZwo+IG9wdGlvbnMsIGFzIHRoZXkgd2VyZSBlYXNpZXIgdG8gY29tcG9zZSBhbmQgbWFpbnRh aW4gdGhhbiBhIGxvb3NlIHBpbGUKPiBvZiBjb21tYW5kbGluZSBhcmd1bWVudHMuCj4gCj4gVGhl IGNvbW1pdCB0ZXh0IGRvZXNuJ3QgZ28gaW50byB0aGUgcmF0aW9uYWxlLCBpbnRlbmRlZCBhdWRp ZW5jZSwgb3IKPiBleHBlY3RlZCB1c2FnZSwgc28gbWF5YmUgbXkgZ3Vlc3NlcyBtaXNzIHRoZSBt YXJrIG9uIHdoYXQgeW91J3JlCj4gdGhpbmtpbmcuCj4gLUV2YW4KClRoZXJlIHdhcyBhIGJyaWVm IGRpc2N1c3Npb24gYWJvdXQgdGhpcyBvbiBKZXNzZSdzIHNlcmllcyBhYm91dCB2ZWN0b3IKdW5h bGlnbmVkIHN1cHBvcnQgWzFdLiBUaGUgb3JpZ2luYWwgaWRlYSB3YXMgdG8gdXNlIFppY2Nsc20g dG8gYWxsb3cKcGVvcGxlIHRvIHNldCB0aGUgdW5hbGlnbmVkIGFjY2VzcyBzcGVlZCBvbiBwcmUt Y29tcGlsZWQgZGlzdHJvIGtlcm5lbHMuCkhvd2V2ZXIgWmljY2xzbSBpc24ndCB1c2VmdWwgc28g dGhlIGFsdGVybmF0aXZlIHJvdXRlIHdhcyB0byB1c2UgYQprZXJuZWwgYXJnLiBUaGVyZSBpcyBh bHJlYWR5IHN1cHBvcnQgZm9yIGEgS2NvbmZpZywgdGhlIGtlcm5lbCBhcmcgaXMKanVzdCBhbm90 aGVyIG9wdGlvbiBmb3IgdXNlcnMuCgpMaW5rOgpodHRwczovL2xvcmUua2VybmVsLm9yZy9sa21s L2FmMzE1MmI2LWFkZjctNDBmYS1iMmExLTg3ZTY2ZWVjNDViMEByaXZvc2luYy5jb20vClsxXQoK LSBDaGFybGllCgoKX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X18KbGludXgtcmlzY3YgbWFpbGluZyBsaXN0CmxpbnV4LXJpc2N2QGxpc3RzLmluZnJhZGVhZC5v cmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcvbWFpbG1hbi9saXN0aW5mby9saW51eC1yaXNj dgo=