From: Thomas Gleixner <tglx@linutronix.de>
To: Marc Zyngier <maz@kernel.org>, Luigi Rizzo <lrizzo@google.com>
Cc: bhelgaas@google.com, linux-kernel@vger.kernel.org
Subject: Re: [patch 1/2] irqchip/msi-lib: Honor the MSI_FLAG_PCI_MSI_MASK_PARENT flag
Date: Thu, 08 Jan 2026 22:32:58 +0100 [thread overview]
Message-ID: <871pjzu6wl.ffs@tglx> (raw)
In-Reply-To: <86ms3amqzm.wl-maz@kernel.org>
On Mon, Dec 22 2025 at 16:16, Marc Zyngier wrote:
>> > > Once we remove the costly readback, is there any remaining reason
>> > > to overwrite [un]mask_irq() with irq_chip_[un]mask_parent() ?
>> >
>> > So you are effectively not masking at all and just rely on hope
>> > instead. I have the utmost confidence in this sort of stuff. Totally.
>>
>> I don't understand the above comment.
>> Masking happens as a result of the PCIe write,
>> which will eventually reach the device. The presence of the
>> readback does nothing to accelerate the landing of the write.
>
> It doesn't accelerate it. It *guarantees* that the write is observed
> and has taken effect. It acts as a completion barrier. Without it, the
> write can be buffered at an arbitrary location in the interconnect, or
> stored in the device but not acted upon.
>
> What you have here is the equivalent of throwing a message in a bottle
> at sea, and expecting a guaranteed reply.
https://xkcd.com/3150/
next prev parent reply other threads:[~2026-01-08 21:33 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-05-17 10:30 [PATCH] irqchip/msi-lib: Honor the MSI_FLAG_PCI_MSI_MASK_PARENT flag Marc Zyngier
2025-05-17 19:59 ` Thomas Gleixner
2025-05-23 9:06 ` Marc Zyngier
2025-06-30 8:59 ` Thomas Gleixner
2025-09-03 14:04 ` [patch 0/2] PCI/MSI: Avoid PCI level masking during normal operation if requested Thomas Gleixner
2025-09-03 14:04 ` [patch 1/2] irqchip/msi-lib: Honor the MSI_FLAG_PCI_MSI_MASK_PARENT flag Thomas Gleixner
2025-09-09 12:47 ` [tip: irq/drivers] " tip-bot2 for Marc Zyngier
2025-12-20 19:31 ` [patch 1/2] " Luigi Rizzo
2025-12-21 11:55 ` Marc Zyngier
2025-12-21 12:41 ` Luigi Rizzo
2025-12-22 16:16 ` Marc Zyngier
2026-01-08 21:32 ` Thomas Gleixner [this message]
2026-01-08 21:55 ` Luigi Rizzo
2026-01-09 12:20 ` Thomas Gleixner
2026-01-09 13:00 ` Luigi Rizzo
2026-01-09 17:01 ` Thomas Gleixner
2025-09-03 14:04 ` [patch 2/2] PCI/MSI: Remove the conditional parent [un]mask logic Thomas Gleixner
2025-09-03 17:38 ` Bjorn Helgaas
2025-09-09 12:47 ` [tip: irq/drivers] " tip-bot2 for Thomas Gleixner
2025-09-09 10:21 ` [patch 0/2] PCI/MSI: Avoid PCI level masking during normal operation if requested Marc Zyngier
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