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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4310ade7c3fsm779077f8f.26.2025.12.16.11.59.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Dec 2025 11:59:14 -0800 (PST) Date: Tue, 16 Dec 2025 19:59:12 +0000 From: David Laight To: "H. Peter Anvin" Cc: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-block@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Paolo Bonzini , Vitaly Kuznetsov , Boris Ostrovsky , xen-devel@lists.xenproject.org, Jean Delvare , Guenter Roeck , Denis Efremov , Jens Axboe Subject: Re: [PATCH 0/5] x86: Cleanups around slow_down_io() Message-ID: <20251216195912.0727cc0d@pumpkin> In-Reply-To: <14EF14B1-8889-4037-8E7B-C8446299B1E9@zytor.com> References: <20251126162018.5676-1-jgross@suse.com> <14EF14B1-8889-4037-8E7B-C8446299B1E9@zytor.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, 16 Dec 2025 07:32:09 -0800 "H. Peter Anvin" wrote: > On December 16, 2025 5:55:54 AM PST, "J=C3=BCrgen Gro=C3=9F" wrote: > >On 16.12.25 14:48, Ingo Molnar wrote: =20 > >>=20 > >> * J=C3=BCrgen Gro=C3=9F wrote: > >> =20 > >>>> CPUs anymore. Should it cause any regressions, it's easy to bisect t= o. > >>>> There's been enough changes around all these facilities that the > >>>> original timings are probably way off already, so we've just been > >>>> cargo-cult porting these to newer kernels essentially. =20 > >>>=20 > >>> Fine with me. > >>>=20 > >>> Which path to removal of io_delay would you (and others) prefer? > >>>=20 > >>> 1. Ripping it out immediately. =20 > >>=20 > >> I'd just rip it out immediately, and see who complains. :-) =20 > > > >I figured this might be a little bit too evil. :-) > > > >I've just sent V2 defaulting to have no delay, so anyone hit by that > >can still fix it by applying the "io_delay" boot parameter. > > > >I'll do the ripping out for kernel 6.21 (or whatever it will be called). > > > > > >Juergen =20 >=20 > Ok, I'm going to veto ripping it out from the real-mode init code, > because I actually know why it is there :) ... Pray tell. One thing I can think of is the delay allows time for a level-sensitive IRQ line to de-assert before an ISR exits. Or, maybe more obscure, to avoid back to back accesses to some register breaking the 'inter-cycle recovery time' for the device. That was a good way to 'break' the Zilog SCC and the 8259 interrupt controller (eg on any reference board with a '286 cpu). David > and that code is pre-UEFI legacy these days anyway. >=20 > Other places... I don't care :) >=20