From: David Laight <David.Laight@ACULAB.COM>
To: 'David Woodhouse' <dwmw2@infradead.org>,
"x86@kernel.org" <x86@kernel.org>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
kvm <kvm@vger.kernel.org>, Dexuan Cui <decui@microsoft.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"maz@misterjones.org" <maz@misterjones.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: RE: [PATCH v3 17/35] x86/pci/xen: Use msi_msg shadow structs
Date: Sun, 25 Oct 2020 13:20:16 +0000 [thread overview]
Message-ID: <340eeca1a7e547bebef694eab505550d@AcuMS.aculab.com> (raw)
In-Reply-To: <a7ed5e550628083199e2747b8267c550689a368c.camel@infradead.org>
From: David Woodhouse
> Sent: 25 October 2020 10:26
> To: David Laight <David.Laight@ACULAB.COM>; x86@kernel.org
>
> On Sun, 2020-10-25 at 09:49 +0000, David Laight wrote:
> > Just looking at a random one of these patches...
> >
> > Does the compiler manage to optimise that reasonably?
> > Or does it generate a lot of shifts and masks as each
> > bitfield is set?
> >
> > The code generation for bitfields is often a lot worse
> > that that for |= setting bits in a word.
>
> Indeed, it appears to be utterly appalling. That was one of my
> motivations for doing it with masks and shifts in the first place.
I thought it would be.
I'm not even sure using bitfields to map hardware registers
makes the code any more readable (or fool proof).
I suspect using #define constants and explicit |= and &= ~
is actually best - provided the names are descriptive enough.
If you set all the fields the compiler will merge the values
and do a single write - provided nothing you read might
alias the target.
The only way to get strongly typed integers is to cast them
to a structure pointer type.
Together with a static inline function to remove the casts
and | the values together it might make things fool proof.
But I've never tried it.
ISTR once doing something like that with error codes, but
it didn't ever make source control.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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next prev parent reply other threads:[~2020-10-25 13:20 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <e6601ff691afb3266e365a91e8b221179daf22c2.camel@infradead.org>
2020-10-24 21:35 ` [PATCH v3 00/35] Fix x2apic enablement and allow more CPUs, clean up I/OAPIC and MSI bitfields David Woodhouse
2020-10-24 21:35 ` [PATCH v3 01/35] x86/apic: Fix x2apic enablement without interrupt remapping David Woodhouse
2020-10-24 21:35 ` [PATCH v3 02/35] x86/msi: Only use high bits of MSI address for DMAR unit David Woodhouse
2020-10-24 21:35 ` [PATCH v3 03/35] x86/apic/uv: Fix inconsistent destination mode David Woodhouse
2020-10-24 21:35 ` [PATCH v3 04/35] x86/devicetree: Fix the ioapic interrupt type table David Woodhouse
2020-10-24 21:35 ` [PATCH v3 05/35] x86/apic: Cleanup delivery mode defines David Woodhouse
2020-10-24 21:35 ` [PATCH v3 06/35] x86/apic: Replace pointless apic::dest_logical usage David Woodhouse
2020-10-24 21:35 ` [PATCH v3 07/35] x86/apic: Get rid of apic::dest_logical David Woodhouse
2020-10-24 21:35 ` [PATCH v3 08/35] x86/apic: Cleanup destination mode David Woodhouse
2020-10-24 21:35 ` [PATCH v3 09/35] x86/apic: Always provide irq_compose_msi_msg() method for vector domain David Woodhouse
2020-10-24 21:35 ` [PATCH v3 10/35] x86/hpet: Move MSI support into hpet.c David Woodhouse
2020-10-24 21:35 ` [PATCH v3 11/35] genirq/msi: Allow shadow declarations of msi_msg::$member David Woodhouse
2020-10-24 21:35 ` [PATCH v3 12/35] x86/msi: Provide msi message shadow structs David Woodhouse
2022-04-06 8:36 ` Reto Buerki
2022-04-06 8:36 ` [PATCH] x86/msi: Fix msi message data shadow struct Reto Buerki
2022-04-06 22:11 ` Thomas Gleixner
2022-04-07 11:06 ` Reto Buerki
2022-04-06 22:07 ` [PATCH v3 12/35] x86/msi: Provide msi message shadow structs Thomas Gleixner
2020-10-24 21:35 ` [PATCH v3 13/35] iommu/intel: Use msi_msg " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 14/35] iommu/amd: " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 15/35] PCI: vmd: " David Woodhouse
2020-10-28 20:49 ` Kees Cook
2020-10-28 21:13 ` Thomas Gleixner
2020-10-28 23:22 ` Kees Cook
2020-10-24 21:35 ` [PATCH v3 16/35] x86/kvm: " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 17/35] x86/pci/xen: " David Woodhouse
2020-10-25 9:49 ` David Laight
2020-10-25 10:26 ` David Woodhouse
2020-10-25 13:20 ` David Laight [this message]
2020-10-24 21:35 ` [PATCH v3 18/35] x86/msi: Remove msidef.h David Woodhouse
2020-10-24 21:35 ` [PATCH v3 19/35] x86/io_apic: Cleanup trigger/polarity helpers David Woodhouse
2020-11-10 6:31 ` Qian Cai
2020-11-10 8:59 ` David Woodhouse
2020-11-10 16:26 ` Paolo Bonzini
2020-10-24 21:35 ` [PATCH v3 20/35] x86/ioapic: Cleanup IO/APIC route entry structs David Woodhouse
2020-10-24 21:35 ` [PATCH v3 21/35] x86/ioapic: Generate RTE directly from parent irqchip's MSI message David Woodhouse
2020-10-24 21:35 ` [PATCH v3 22/35] genirq/irqdomain: Implement get_name() method on irqchip fwnodes David Woodhouse
2020-10-25 9:41 ` Marc Zyngier
2020-10-24 21:35 ` [PATCH v3 23/35] x86/apic: Add select() method on vector irqdomain David Woodhouse
2020-10-24 21:35 ` [PATCH v3 24/35] iommu/amd: Implement select() method on remapping irqdomain David Woodhouse
2020-10-24 21:35 ` [PATCH v3 25/35] iommu/vt-d: " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 26/35] iommu/hyper-v: " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 27/35] x86/hpet: Use irq_find_matching_fwspec() to find " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 28/35] x86/ioapic: " David Woodhouse
2020-10-24 21:35 ` [PATCH v3 29/35] x86: Kill all traces of irq_remapping_get_irq_domain() David Woodhouse
2020-10-24 21:35 ` [PATCH v3 30/35] iommu/vt-d: Simplify intel_irq_remapping_select() David Woodhouse
2020-10-24 21:35 ` [PATCH v3 31/35] x86/ioapic: Handle Extended Destination ID field in RTE David Woodhouse
2020-10-24 21:35 ` [PATCH v3 32/35] x86/apic: Support 15 bits of APIC ID in MSI where available David Woodhouse
2020-10-24 21:35 ` [PATCH v3 33/35] iommu/hyper-v: Disable IRQ pseudo-remapping if 15 bit APIC IDs are available David Woodhouse
2020-10-24 21:35 ` [PATCH v3 34/35] x86/kvm: Reserve KVM_FEATURE_MSI_EXT_DEST_ID David Woodhouse
2020-10-24 21:35 ` [PATCH v3 35/35] x86/kvm: Enable 15-bit extension when KVM_FEATURE_MSI_EXT_DEST_ID detected David Woodhouse
2020-10-25 8:12 ` [PATCH v3 00/35] Fix x2apic enablement and allow more CPUs, clean up I/OAPIC and MSI bitfields David Woodhouse
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