Re: Proposal: Delegating Exceptions from VS-mode or VU-mode to U-mode


Anup Patel
 

Hi,

 

The context switching overhead for VirtIO interrupts that this proposal is trying to solve is already solved across architectures by:

  1. KVM in-kernel VirtIO backends emulation (i.e. VHost) (Already available)
  2. KVM in-kernel interrupt-controller emulation and KVM irqfd (Available on other architectures but not currently available for KVM RISC-V)

 

The point2 is intentionally not done for KVM RISC-V because we don’t want in-kernel PLIC emulation due to lack of MSI support and Virtualization support in PLIC. Also, the in-kernel PLIC emulation will become redundant once new interrupt controller spec is available. We will go for in-kernel interrupt controller emulation once new interrupt controller spec is available.

 

Is there any other advantage of this proposal over VHost + In-kernel interrupt-controller ??

 

Regards,

Anup

 

From: tech-privileged@... <tech-privileged@...> On Behalf Of Yifei Jiang via lists.riscv.org
Sent: 18 September 2020 13:33
To: tech-privileged@...
Subject: [RISC-V] [tech-privileged] Proposal: Delegating Exceptions from VS-mode or VU-mode to U-mode

 

Hi all,

 

In this proposal, we extended N extension and applied it to H extension for improving the performance of virtual I/O devices in the virtualization scenario. We proposed a new mechanism to delegate exceptions from VS-mode/VU-mode to U-mode. A solution is also implemented based on QEMU simulator and KVM virtualization architecture. Evaluation results show that our proposal achieves nearly 2x faster synchronous I/O processing speed than the orginal system.

 

The attachment is the detailed proposal. Any comments are welcome.

 

Regards,

Yifei

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