From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751245AbeEVJOM (ORCPT ); Tue, 22 May 2018 05:14:12 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:38537 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750707AbeEVJOL (ORCPT ); Tue, 22 May 2018 05:14:11 -0400 Date: Tue, 22 May 2018 11:14:08 +0200 From: Sebastian Andrzej Siewior To: Mike Galbraith Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH] x86: UV: raw_spinlock conversion Message-ID: <20180522091408.nt4fodr4f5ikk5ow@linutronix.de> References: <20180504111459.24825-1-bigeasy@linutronix.de> <20180504111459.24825-2-bigeasy@linutronix.de> <1525604359.28142.3.camel@gmx.de> <20180507073928.shmtfpqyhgxya53b@linutronix.de> <1526738996.5365.1.camel@gmx.de> <20180522065051.xy42nwvcxz2nekti@linutronix.de> <1526977462.6491.1.camel@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1526977462.6491.1.camel@gmx.de> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-05-22 10:24:22 [+0200], Mike Galbraith wrote: > On Tue, 2018-05-22 at 08:50 +0200, Sebastian Andrzej Siewior wrote: > > > > Regarding the preempt_disable() in the original patch in uv_read_rtc(): > > This looks essential for PREEMPT configs. Is it possible to get this > > tested by someone or else get rid of the UV code? It looks broken for > > "uv_get_min_hub_revision_id() != 1". > > I suspect SGI cares not one whit about PREEMPT. so it is broken then. I leave it to the x86 maintainers but on the very least it should depend on !PREEMPT (if not server). > > Why does PREEMPT_RT require migrate_disable() but PREEMPT only is fine > > as-is? This does not look right. > > UV is not ok with a PREEMPT config, it's just that for RT it's dirt > simple to shut it up, whereas for PREEMPT, preempt_disable() across > uv_bau_init() doesn't cut it due to allocations, and whatever else I > would have met before ending the whack-a-mole game. > > If I were in your shoes, I think I'd just stop caring about UV until a > real user appears. AFAIK, I'm the only guy who ever ran RT on UV, and > I only did so because SUSE asked me to look into it.. years ago now. Okay. The problem I have with this patch is that it remains RT only while the problem it addresses is not RT-only and PREEMPT kernels are very much affected. The thing is that *you* are my only UV user :) If you suggest that I should stop caring about UV than I do so. Please post a patch that adds a dependency to UV on PREEMPT so that part of the architecture is documented. > -Mike Sebastian