From: Thomas Gleixner <tglx@linutronix.de>
To: David Woodhouse <dwmw2@infradead.org>,
Dexuan Cui <decui@microsoft.com>, Ming Lei <ming.lei@redhat.com>,
Christoph Hellwig <hch@lst.de>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Stefan Haberland <sth@linux.vnet.ibm.com>,
Jens Axboe <axboe@kernel.dk>, Marc Zyngier <marc.zyngier@arm.com>,
"linux-pci\@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Long Li <longli@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Michael Kelley <mikelley@microsoft.com>
Subject: Re: irq_build_affinity_masks() allocates improper affinity if num_possible_cpus() > num_present_cpus()?
Date: Tue, 06 Oct 2020 21:00:24 +0200 [thread overview]
Message-ID: <87h7r76uyf.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <65ba8a8b86201d8906313fbacc4fb711b9b423af.camel@infradead.org>
On Tue, Oct 06 2020 at 09:37, David Woodhouse wrote:
> On Tue, 2020-10-06 at 06:47 +0000, Dexuan Cui wrote:
>> PS2, the latest Hyper-V provides only one ACPI MADT entry to a 1-CPU VM,
>> so the issue described above can not reproduce there.
>
> It seems fairly easy to reproduce in qemu with -smp 1,maxcpus=128 and a
> virtio-blk drive, having commented out the 'desc->pre_vectors++' around
> line 130 of virtio_pci_common.c so that it does actually spread them.
>
> [ 0.836252] i=0, affi = 0,65-127
> [ 0.836672] i=1, affi = 1-64
> [ 0.837905] virtio_blk virtio1: [vda] 41943040 512-byte logical blocks (21.5 GB/20.0 GiB)
> [ 0.839080] vda: detected capacity change from 0 to 21474836480
>
> In my build I had to add 'nox2apic' because I think I actually already
> fixed this for the x2apic + no-irq-remapping case with the max_affinity
> patch series¹. But mostly by accident.
There is nothing to fix. It's intentional behaviour. Managed interrupts
and their spreading (aside of the rather odd spread here) work that way.
And virtio-blk works perfectly fine with that.
Thanks,
tglx
next prev parent reply other threads:[~2020-10-06 19:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-06 6:47 irq_build_affinity_masks() allocates improper affinity if num_possible_cpus() > num_present_cpus()? Dexuan Cui
2020-10-06 8:37 ` David Woodhouse
2020-10-06 11:17 ` David Woodhouse
2020-10-06 19:00 ` Thomas Gleixner [this message]
2020-10-06 18:57 ` Thomas Gleixner
2020-10-07 3:08 ` Dexuan Cui
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