From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: Arches that don't support PREEMPT Date: Tue, 19 Sep 2023 07:50:36 -0700 Message-ID: <7EB81196-3A32-4638-A076-0C0CFF722996@zytor.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-ID:References: In-Reply-To:Subject:CC:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=faUiEGRpypN0eR3wuQp71okWlg+ed77cY2poRYumr5c=; b=HnPx4nnJfTlfdy dr4ccZUxH2e+UyxWjbp1nmnf0bl3bbB6FP2UKLICJTxUAmgCrA2oDxjeTIlXCYcemsjNldZZu8M2c QJLHzPzbEXQZOZMPtQYdn+HYipVpl9UVsePjAu6tXZhuMi6Q4EmX1/3i4uBiMgOwYKee96hb27IUM zra2vvguU45vMvmOXCHDQ5NVMqSvqxtxVhSIq59qXLaEaA0eovrhDJfoTkHnRdUAPtJwonKZQTX2U 9Ot4lnl5ZQRnZYrxoR6Y+d0p40qLS/JCrzqEX0wZIjC8oQcpmszQSHVkBdQzSXneaL+9zZGYEcOvr zskmwkYcrI6H2fea8Sjg==; DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 38JEoefQ2134063 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2023091101; t=1695135044; bh=tUr/tHfO1etLyJ5iEsuuEqfdyv68/fcilJS639sYECk=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=rKxd+En5VITJVOEGiLmUKlIHqjSXGvGPVilskDP5cDHYQFDKWK93NnuXqpVPm85sg IQ8mukavFvwyuQ2+LZQx/SFeLAJwt3NRGCnufaQHbyTI8yWPctJU8mvsKC8ydIURew TWPjynPQFVYSogaCk173v4hcW64i46jcQU9Kvle5dlPXtXvcQsapqcrc0+JX4lPkGr sf4WDdKOaq1+eQt1DQ0rhsH9vVqYCi8L00mlI3ZyOafcEgEQnuvBKUCD1TlG5Gwolf v/ICNSdydZcPDXpEjwZCuJJ1aG9hOBj/BpI/RLMLoqn1ibICPlO3SW2Zd9eA3bsF4x ffTTSTGuqyWmA== In-Reply-To: <877comw8m7.ffs@tglx> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+glud-user-mode-linux-devel=m.gmane-mx.org@lists.infradead.org To: Thomas Gleixner , John Paul Adrian Glaubitz , Peter Zijlstra Cc: 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 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 other 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 with the >> architectures lacking CONFIG_PREEMPT at the moment. This seems to be more >> something about organizing KConfig files. >> >> I find it a bit unfair that maintainers of architectures that have huge 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 keep 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?