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Tue, 19 Sep 2023 07:57:36 -0700 (PDT) MIME-Version: 1.0 References: <87zg1u1h5t.fsf@oracle.com> <20230911150410.GC9098@noisy.programming.kicks-ass.net> <87h6o01w1a.fsf@oracle.com> <20230912082606.GB35261@noisy.programming.kicks-ass.net> <87cyyfxd4k.ffs@tglx> <87led2wdj0.ffs@tglx> <0e69f7df80dc5878071deb0d80938138d19de1d1.camel@physik.fu-berlin.de> <20230919134218.GA39281@noisy.programming.kicks-ass.net> <877comw8m7.ffs@tglx> <7EB81196-3A32-4638-A076-0C0CFF722996@zytor.com> In-Reply-To: <7EB81196-3A32-4638-A076-0C0CFF722996@zytor.com> From: Matt Turner Date: Tue, 19 Sep 2023 10:57:24 -0400 Message-ID: Subject: Re: Arches that don't support PREEMPT To: "H. Peter Anvin" Cc: Thomas Gleixner , John Paul Adrian Glaubitz , Peter Zijlstra , Matthew Wilcox , Linus Torvalds , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, mgorman@suse.de, rostedt@goodmis.org, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, Geert Uytterhoeven , linux-m68k@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Brian Cain , linux-hexagon@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , linux-alpha@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: wdybfkcih8rgrsjrt7hnbxgy838fmgt7 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5E71918001F X-Rspam-User: X-HE-Tag: 1695135457-871 X-HE-Meta: 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 J9uuY3lQ /l87kRA4JuS+X6aHQ8visskz4Tzb8oPbJi4TymDH3AE/jFrtvIUa4KHox5wB5sFAR4BvzZCbhkRz2Nb1Lu2IJySxLBBva/aNtEo2eRi9lYNgCUnbqgMcXALFO6ZHsRETJOChGG5qknZy7BVCkultA2nsUlN8M/L+LKoKGDb96IQdKGoQDiNfuejWE2PKVuLzH74yqkw1WMe21ShUokoy79yNGnEJn9LkyKfXqF/jz6bxxk1ZkzmRr/Qqdm4MCspaI1Ny+VenoIqF4B/vD48YVZG7N0akkyYtOEtCk7Qdm2P/oKzRkxM5MsYheV/4TAlJipLJMPAdHFsTmOpS2r7vqWIEOjNk1XSpMXgzvpgWbDSHkDQxLzOvkWJfsLijgsIo5VcFt4ZtM6LKj36EO+AnPPuXaB/jSKSKrTx3zS/xv64c1fElpoCCOUw0OBw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 19, 2023 at 10:51=E2=80=AFAM H. Peter Anvin wro= te: > > On September 19, 2023 7:17:04 AM PDT, Thomas Gleixner wrote: > >On Tue, Sep 19 2023 at 15:48, John Paul Adrian Glaubitz wrote: > >> On Tue, 2023-09-19 at 15:42 +0200, Peter Zijlstra wrote: > >>> > The agreement to kill off ia64 wasn't an invitation to kill off oth= er stuff > >>> > that people are still working on! Can we please not do this? > >>> > >>> If you're working on one of them, then surely it's a simple matter of > >>> working on adding CONFIG_PREEMPT support :-) > >> > >> As Geert poined out, I'm not seeing anything particular problematic wi= th the > >> architectures lacking CONFIG_PREEMPT at the moment. This seems to be m= ore > >> something about organizing KConfig files. > >> > >> I find it a bit unfair that maintainers of architectures that have hug= e companies > >> behind them use their manpower to urge less popular architectures for = removal just > >> because they don't have 150 people working on the port so they can kee= p up with > >> design changes quickly. > > > >I don't urge for removal. I just noticed that these four architectures > >lack PREEMPT support. The only thing which is missing is the actual > >preemption point in the return to kernel code path. > > > >But otherwise it should just work, which I obviously can't confirm :) > > > >Even without that preemption point it should build and boot. There might > >be some minor latency issues when that preemption point is not there, > >but adding it is not rocket science either. It's probably about 10 lines > >of ASM code, if at all. > > > >Though not adding that might cause a blocking issue for the rework of > >the whole preemption logic in order to remove the sprinkled around > >cond_resched() muck or force us to maintain some nasty workaround just > >for the benefit of a few stranglers. > > > >So I can make the same argument the other way around, that it's > >unjustified that some architectures which are just supported for > >nostalgia throw roadblocks into kernel developemnt. > > > >If my ALPHA foo wouldn't be very close to zero, I'd write that ASM hack > >myself, but that's going to cost more of my and your time than it's > >worth the trouble, > > > >Hmm. I could delegate that to Linus, he might still remember :) > > > >Thanks, > > > > tglx > > Does *anyone* actually run Alpha at this point? I do, as part of maintaining the Gentoo distribution for Alpha. I'm listed in MAINTAINERS, but really only so I can collect patches send them to Linus after testing. I don't have copious amounts of free time to be proactive in kernel development and it's also not really my area of expertise so I'm nowhere near effective at it. I would be happy to test any patches sent my way (but I acknowledge that writing these patches wouldn't be high on anyone's priority list, etc) (A video my friend Ian and I made about a particularly large AlphaServer I have in my basement, in case anyone is interested: https://www.youtube.com/watch?v=3Dz658a8Js5qg)