Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:3 as permitted sender) client-ip=2620:137:e000::3:3;
Message-ID: <de98424d-41f9-90f9-742d-623e2b55c564@cambridgegreys.com>
Date:   Tue, 19 Sep 2023 17:41:21 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.10.0
Subject: Re: Arches that don't support PREEMPT
Content-Language: en-US
To:     Richard Weinberger <richard@nod.at>
Cc:     tglx <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        Matthew Wilcox <willy@infradead.org>,
        torvalds <torvalds@linux-foundation.org>,
        Ankur Arora <ankur.a.arora@oracle.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, x86 <x86@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>, bp <bp@alien8.de>,
        dave hansen <dave.hansen@linux.intel.com>, hpa <hpa@zytor.com>,
        mingo <mingo@redhat.com>, juri lelli <juri.lelli@redhat.com>,
        vincent guittot <vincent.guittot@linaro.org>, mgorman@suse.de,
        Steven Rostedt <rostedt@goodmis.org>,
        jon grimm <jon.grimm@amd.com>, bharata@amd.com,
        raghavendra kt <raghavendra.kt@amd.com>,
        boris ostrovsky <boris.ostrovsky@oracle.com>,
        konrad wilk <konrad.wilk@oracle.com>, jgross <jgross@suse.com>,
        andrew cooper3 <andrew.cooper3@citrix.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um <linux-um@lists.infradead.org>,
        Brian Cain <bcain@quicinc.com>, linux-hexagon@vger.kernel.org,
        Richard Henderson <richard.henderson@linaro.org>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Matt Turner <mattst88@gmail.com>,
        linux-alpha <linux-alpha@vger.kernel.org>
References: <87zg1u1h5t.fsf@oracle.com> <87led2wdj0.ffs@tglx>
 <ZQmbhoQIINs8rLHp@casper.infradead.org>
 <0e69f7df80dc5878071deb0d80938138d19de1d1.camel@physik.fu-berlin.de>
 <20230919134218.GA39281@noisy.programming.kicks-ass.net>
 <bd664a61-4506-bab0-19c3-0011f57005b5@cambridgegreys.com>
 <87y1h2ur98.ffs@tglx>
 <9a5c0856-d542-9912-7494-53d7fe4538a3@cambridgegreys.com>
 <551475267.58816.1695140566849.JavaMail.zimbra@nod.at>
From:   Anton Ivanov <anton.ivanov@cambridgegreys.com>
In-Reply-To: <551475267.58816.1695140566849.JavaMail.zimbra@nod.at>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 19/09/2023 17:22, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "anton ivanov" <anton.ivanov@cambridgegreys.com>
>> It's been a while. I remember that I dropped it at the time, but do not remember
>> the full details.
>>
>> There was some stuff related to FP state and a few other issues I ran into while
>> rewriting the interrupt controller. Some of it may be resolved by now as we are
>> using host cpu flags, etc.
> 
> I remember also having a hacky but working version almost 10 years ago.
> It was horrible slow because of the extra scheduler rounds.
> But yes, if PREEMPT will be a must-have feature we'll have to try again.

We will need proper fpu primitives for starters that's for sure. fpu_star/end in UML are presently NOOP.

Some of the default spinlocks and other stuff which we pick up from generic may need to change as well.

This is off the top of my head and something which we can fix straight away. I will send some patches to the mailing list tomorrow or on Thu.

A.

> 
> Thanks,
> //richard
> 
> _______________________________________________
> linux-um mailing list
> linux-um@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-um

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/