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Re: [Qemu-devel] [PATCH v5 00/18] IOMMU: Enable interrupt remapping for
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v5 00/18] IOMMU: Enable interrupt remapping for Intel IOMMU |
Date: |
Mon, 9 May 2016 13:50:26 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 |
On 03/05/2016 06:38, Jan Kiszka wrote:
> Yes, this doesn't look good from the performance POV. Given that most
> EOIs of the APICs will not trigger a message to an IOAPIC and userspace
> exits are expensive, that should be measurable.
>
> But you should optimize route updating a bit: I noticed real delays
> (almost a second) when reprogramming all IOAPIC pins during Jailhouse
> handover. That's because of the heavyweight synchronize_srcu we have on
> each route change. Even if that is an extreme case, you should try to
> reduce route updates to only those that were actually affected by an
> IRTE change.
It's okay to make it synchronize_srcu_expedited. Unlike RCU, expediting
SRCU grace periods doesn't have an impact on the whole system (the
reason why KVM uses SRCU here is exactly to avoid
synchronize_rcu_expedited).
Of course, optimizing userspace cannot hurt either.
Paolo