Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.36 as permitted sender) client-ip=23.128.96.36;
Message-ID: <9a5c0856-d542-9912-7494-53d7fe4538a3@cambridgegreys.com>
Date:   Tue, 19 Sep 2023 16:21:29 +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:     Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ankur Arora <ankur.a.arora@oracle.com>,
        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, hpa@zytor.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 <geert@linux-m68k.org>,
        linux-m68k@lists.linux-m68k.org,
        Richard Weinberger <richard@nod.at>,
        Johannes Berg <johannes@sipsolutions.net>,
        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@vger.kernel.org
References: <87zg1u1h5t.fsf@oracle.com>
 <CAHk-=whMkp68vNxVn1H3qe_P7n=X2sWPL9kvW22dsvMFH8FcQQ@mail.gmail.com>
 <20230911150410.GC9098@noisy.programming.kicks-ass.net>
 <87h6o01w1a.fsf@oracle.com>
 <20230912082606.GB35261@noisy.programming.kicks-ass.net>
 <87cyyfxd4k.ffs@tglx>
 <CAHk-=whnwC01m_1f-gaM1xbvvwzwTiKitrWniA-ChZv+bM03dg@mail.gmail.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>
From:   Anton Ivanov <anton.ivanov@cambridgegreys.com>
In-Reply-To: <87y1h2ur98.ffs@tglx>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 19/09/2023 16:17, Thomas Gleixner wrote:
> On Tue, Sep 19 2023 at 15:21, Anton Ivanov wrote:
>> On 19/09/2023 14:42, Peter Zijlstra wrote:
>>> If you're working on one of them, then surely it's a simple matter of
>>> working on adding CONFIG_PREEMPT support :-)
>> In the case of UML adding preempt will be quite difficult. I looked at
>> this a few years back.
> What's so difficult about it?

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 can give it another go :)

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