linux-kernel - Re: [PATCH] PCI MSI: allow alignment restrictions on vector allocation

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Message-ID: <alpine.DEB.2.20.1710032306170.2278@nanos>
Date:   Tue, 3 Oct 2017 23:07:58 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Daniel Drake <drake@...lessm.com>
cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org, linux-wireless@...r.kernel.org,
        ath9k-devel@....qualcomm.com, linux@...lessm.com
Subject: Re: [PATCH] PCI MSI: allow alignment restrictions on vector
 allocation

On Mon, 2 Oct 2017, Thomas Gleixner wrote:
> On Mon, 2 Oct 2017, Thomas Gleixner wrote:
> > On Mon, 2 Oct 2017, Daniel Drake wrote:
> >   2) The affinity setting of straight MSI interrupts (w/o remapping) on x86
> >      requires to make the affinity change from the interrupt context of the
> >      current active vector in order not to lose interrupts or worst case
> >      getting into a stale state.
> > 
> >      That works for single vectors, but trying to move all vectors in one
> >      go is more or less impossible, as there is no reliable way to
> >      determine that none of the other vectors is on flight.
> > 
> >      There might be some 'workarounds' for that, but I rather avoid that
> >      unless we get an official documented one from Intel/AMD.
> 
> Thinking more about it. That might be actually a non issue for MSI, but we
> have that modus operandi in the current code and we need to address that
> first before even thinking about multi MSI support.

But even if its possible, it's very debatable whether it's worth the effort
when this driver just can use the legacy INTx.and be done with it.

Thanks,

	tglx