From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v2 26/28] arm64/sve: Add documentation Date: Mon, 09 Oct 2017 15:07:23 +0100 Message-ID: <87376sbejo.fsf@linaro.org> References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-27-git-send-email-Dave.Martin@arm.com> <59D7A4AF.40408@arm.com> <20171006173715.GC3611@e103592.cambridge.arm.com> <878tgkbr6m.fsf@linaro.org> <20171009094930.GD3611@e103592.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail-wm0-f43.google.com ([74.125.82.43]:54259 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754125AbdJIOH0 (ORCPT ); Mon, 9 Oct 2017 10:07:26 -0400 Received: by mail-wm0-f43.google.com with SMTP id q132so23825706wmd.2 for ; Mon, 09 Oct 2017 07:07:25 -0700 (PDT) In-reply-to: <20171009094930.GD3611@e103592.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Martin Cc: linux-arch@vger.kernel.org, Mark Rutland , libc-alpha@sourceware.org, Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Will Deacon , Richard Sandiford nd@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Dave Martin writes: > On Mon, Oct 09, 2017 at 10:34:25AM +0100, Alex Benn=C3=A9e wrote: >> >> Dave Martin writes: >> >> > On Fri, Oct 06, 2017 at 04:43:43PM +0100, Szabolcs Nagy wrote: >> >> On 31/08/17 18:00, Dave Martin wrote: >> >> > +9. System runtime configuration >> >> > +-------------------------------- >> >> > + >> >> > +* To mitigate the ABI impact of expansion of the signal frame, a p= olicy >> >> > + mechanism is provided for administrators, distro maintainers and= developers >> >> > + to set the default vector length for userspace processes: >> >> > + >> >> > +/proc/cpu/sve_default_vector_length >> >> >> >> >> >> elsewhere in the patch series i see >> >> >> >> /proc/sys/abi/sve_default_vector_length >> >> >> >> is this supposed to be the same? >> > >> > Good spot, thanks! >> > >> > /proc/cpu/ was the old location: they should both say /proc/abi/. >> > I'll fix it. >> >> Isn't /sys (or rather sysfs) the preferred location for modern control >> knobs that mirror the kernels object model or is SVE a special case for >> extending /proc? > > I couldn't figure out which kernel object this maps to. There's no > device, no driver. This isn't even per-cpu. Hmm I can see: /sys/devices/system/cpu On both my x86 and arm64 systems - but I guess this is more ABIish than CPU feature related. > sysctl is already used for similar knobs to this one, so I followed that > precedent -- though if someone argues strongly enough it could be > changed. > > Are there already examples of arch controls like this in sysfs? I > wasn't aware of any, but I didn't look all that hard... Given the paucity of the /proc/sys/abi on both systems I guess this sort of knob is rare enough that people haven't expressed a strong preference for sysfs here. I have no objection to staying with /proc/sys/abi/. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f43.google.com ([74.125.82.43]:54259 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754125AbdJIOH0 (ORCPT ); Mon, 9 Oct 2017 10:07:26 -0400 Received: by mail-wm0-f43.google.com with SMTP id q132so23825706wmd.2 for ; Mon, 09 Oct 2017 07:07:25 -0700 (PDT) References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-27-git-send-email-Dave.Martin@arm.com> <59D7A4AF.40408@arm.com> <20171006173715.GC3611@e103592.cambridge.arm.com> <878tgkbr6m.fsf@linaro.org> <20171009094930.GD3611@e103592.cambridge.arm.com> From: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v2 26/28] arm64/sve: Add documentation In-reply-to: <20171009094930.GD3611@e103592.cambridge.arm.com> Date: Mon, 09 Oct 2017 15:07:23 +0100 Message-ID: <87376sbejo.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Martin Cc: linux-arch@vger.kernel.org, Mark Rutland , libc-alpha@sourceware.org, Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Will Deacon , Richard Sandiford nd@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Message-ID: <20171009140723.8nq_z_RNA1pXhOflTQTVj7I7Lf65mQzXmdqoBbJFpOs@z> Dave Martin writes: > On Mon, Oct 09, 2017 at 10:34:25AM +0100, Alex Benn=C3=A9e wrote: >> >> Dave Martin writes: >> >> > On Fri, Oct 06, 2017 at 04:43:43PM +0100, Szabolcs Nagy wrote: >> >> On 31/08/17 18:00, Dave Martin wrote: >> >> > +9. System runtime configuration >> >> > +-------------------------------- >> >> > + >> >> > +* To mitigate the ABI impact of expansion of the signal frame, a p= olicy >> >> > + mechanism is provided for administrators, distro maintainers and= developers >> >> > + to set the default vector length for userspace processes: >> >> > + >> >> > +/proc/cpu/sve_default_vector_length >> >> >> >> >> >> elsewhere in the patch series i see >> >> >> >> /proc/sys/abi/sve_default_vector_length >> >> >> >> is this supposed to be the same? >> > >> > Good spot, thanks! >> > >> > /proc/cpu/ was the old location: they should both say /proc/abi/. >> > I'll fix it. >> >> Isn't /sys (or rather sysfs) the preferred location for modern control >> knobs that mirror the kernels object model or is SVE a special case for >> extending /proc? > > I couldn't figure out which kernel object this maps to. There's no > device, no driver. This isn't even per-cpu. Hmm I can see: /sys/devices/system/cpu On both my x86 and arm64 systems - but I guess this is more ABIish than CPU feature related. > sysctl is already used for similar knobs to this one, so I followed that > precedent -- though if someone argues strongly enough it could be > changed. > > Are there already examples of arch controls like this in sysfs? I > wasn't aware of any, but I didn't look all that hard... Given the paucity of the /proc/sys/abi on both systems I guess this sort of knob is rare enough that people haven't expressed a strong preference for sysfs here. I have no objection to staying with /proc/sys/abi/. -- Alex Benn=C3=A9e