From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Honig <ahonig@google.com>
Subject: Re: [RFC PATCH 1/4] KVM: x86: Split the APIC from the rest of IRQCHIP.
Date: Thu, 14 May 2015 12:29:21 -0700
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Cc: Steve Rutherford <srutherford@google.com>,
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To: "Wu, Feng" <feng.wu@intel.com>
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>
> BTW, what is the purpose of this series. If I understand it correctly, you only want to
> use the in-kernel lapic and leave the others (pic, ioapic) in userspace, what is the
> benefit of it?

The purpose is to achieve the security benefit of removing some of the
interrupt handling into userspace, without incurring a significant
performance penalty.  If you move the entire IRQCHIP into userspace,
we've seen perf impacts from 15-200% depending on the workload.  With
this patch series, we're seeing perf penalty <1% on our tests (TCP_RR
latency, TCP throughput, and Disk I/O).  See
(https://lwn.net/Articles/619332/)

>
> Thanks,
> Feng
>
>>