[PATCH v3 00/41] Optimize KVM/ARM for VHE systems
Tomasz Nowicki
tn at semihalf.com
Thu Feb 1 05:57:59 PST 2018
Hi Christoffer,
I created simple module for VM kernel. It is spinning on PSCI version
hypercall to measure the base exit cost as you suggested. Also, I
measured CPU cycles for each loop and here are my results:
My setup:
1-socket ThunderX2 running VM - 1VCPU
Tested baselines:
a) host kernel v4.15-rc3 and VM kernel v4.15-rc3
b) host kernel v4.15-rc3 + vhe-optimize-v3-with-fixes and VM kernel
v4.15-rc3
Module was loaded from VM and the results are presented in [%] relative
to average CPU cycles spending on PSCI version hypercall for vanilla VHE
host kernel v4.15-rc3:
VHE | nVHE
=========================
baseline a) 100% | 130%
=========================
baseline a) 36% | 123%
So I confirm significant performance improvement, especially for VHE
case. Additionally, I run network throughput tests with vhost-net but
for that case no differences.
Thanks,
Tomasz
On 12.01.2018 13:07, Christoffer Dall wrote:
> This series redesigns parts of KVM/ARM to optimize the performance on
> VHE systems. The general approach is to try to do as little work as
> possible when transitioning between the VM and the hypervisor. This has
> the benefit of lower latency when waiting for interrupts and delivering
> virtual interrupts, and reduces the overhead of emulating behavior and
> I/O in the host kernel.
>
> Patches 01 through 06 are not VHE specific, but rework parts of KVM/ARM
> that can be generally improved. We then add infrastructure to move more
> logic into vcpu_load and vcpu_put, we improve handling of VFP and debug
> registers.
>
> We then introduce a new world-switch function for VHE systems, which we
> can tweak and optimize for VHE systems. To do that, we rework a lot of
> the system register save/restore handling and emulation code that may
> need access to system registers, so that we can defer as many system
> register save/restore operations to vcpu_load and vcpu_put, and move
> this logic out of the VHE world switch function.
>
> We then optimize the configuration of traps. On non-VHE systems, both
> the host and VM kernels run in EL1, but because the host kernel should
> have full access to the underlying hardware, but the VM kernel should
> not, we essentially make the host kernel more privileged than the VM
> kernel despite them both running at the same privilege level by enabling
> VE traps when entering the VM and disabling those traps when exiting the
> VM. On VHE systems, the host kernel runs in EL2 and has full access to
> the hardware (as much as allowed by secure side software), and is
> unaffected by the trap configuration. That means we can configure the
> traps for VMs running in EL1 once, and don't have to switch them on and
> off for every entry/exit to/from the VM.
>
> Finally, we improve our VGIC handling by moving all save/restore logic
> out of the VHE world-switch, and we make it possible to truly only
> evaluate if the AP list is empty and not do *any* VGIC work if that is
> the case, and only do the minimal amount of work required in the course
> of the VGIC processing when we have virtual interrupts in flight.
>
> The patches are based on v4.15-rc3, v9 of the level-triggered mapped
> interrupts support series [1], and the first five patches of James' SDEI
> series [2].
>
> I've given the patches a fair amount of testing on Thunder-X, Mustang,
> Seattle, and TC2 (32-bit) for non-VHE testing, and tested VHE
> functionality on the Foundation model, running both 64-bit VMs and
> 32-bit VMs side-by-side and using both GICv3-on-GICv3 and
> GICv2-on-GICv3.
>
> The patches are also available in the vhe-optimize-v3 branch on my
> kernel.org repository [3]. The vhe-optimize-v3-base branch contains
> prerequisites of this series.
>
> Changes since v2:
> - Rebased on v4.15-rc3.
> - Includes two additional patches that only does vcpu_load after
> kvm_vcpu_first_run_init and only for KVM_RUN.
> - Addressed review comments from v2 (detailed changelogs are in the
> individual patches).
>
> Thanks,
> -Christoffer
>
> [1]: git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git level-mapped-v9
> [2]: git://linux-arm.org/linux-jm.git sdei/v5/base
> [3]: git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git vhe-optimize-v3
>
> Christoffer Dall (40):
> KVM: arm/arm64: Avoid vcpu_load for other vcpu ioctls than KVM_RUN
> KVM: arm/arm64: Move vcpu_load call after kvm_vcpu_first_run_init
> KVM: arm64: Avoid storing the vcpu pointer on the stack
> KVM: arm64: Rework hyp_panic for VHE and non-VHE
> KVM: arm/arm64: Get rid of vcpu->arch.irq_lines
> KVM: arm/arm64: Add kvm_vcpu_load_sysregs and kvm_vcpu_put_sysregs
> KVM: arm/arm64: Introduce vcpu_el1_is_32bit
> KVM: arm64: Defer restoring host VFP state to vcpu_put
> KVM: arm64: Move debug dirty flag calculation out of world switch
> KVM: arm64: Slightly improve debug save/restore functions
> KVM: arm64: Improve debug register save/restore flow
> KVM: arm64: Factor out fault info population and gic workarounds
> KVM: arm64: Introduce VHE-specific kvm_vcpu_run
> KVM: arm64: Remove kern_hyp_va() use in VHE switch function
> KVM: arm64: Don't deactivate VM on VHE systems
> KVM: arm64: Remove noop calls to timer save/restore from VHE switch
> KVM: arm64: Move userspace system registers into separate function
> KVM: arm64: Rewrite sysreg alternatives to static keys
> KVM: arm64: Introduce separate VHE/non-VHE sysreg save/restore
> functions
> KVM: arm/arm64: Remove leftover comment from kvm_vcpu_run_vhe
> KVM: arm64: Unify non-VHE host/guest sysreg save and restore functions
> KVM: arm64: Don't save the host ELR_EL2 and SPSR_EL2 on VHE systems
> KVM: arm64: Change 32-bit handling of VM system registers
> KVM: arm64: Rewrite system register accessors to read/write functions
> KVM: arm64: Introduce framework for accessing deferred sysregs
> KVM: arm/arm64: Prepare to handle deferred save/restore of SPSR_EL1
> KVM: arm64: Prepare to handle deferred save/restore of ELR_EL1
> KVM: arm64: Defer saving/restoring 64-bit sysregs to vcpu load/put on
> VHE
> KVM: arm64: Prepare to handle deferred save/restore of 32-bit
> registers
> KVM: arm64: Defer saving/restoring 32-bit sysregs to vcpu load/put
> KVM: arm64: Move common VHE/non-VHE trap config in separate functions
> KVM: arm64: Configure FPSIMD traps on vcpu load/put
> KVM: arm64: Configure c15, PMU, and debug register traps on cpu
> load/put for VHE
> KVM: arm64: Separate activate_traps and deactive_traps for VHE and
> non-VHE
> KVM: arm/arm64: Get rid of vgic_elrsr
> KVM: arm/arm64: Handle VGICv2 save/restore from the main VGIC code
> KVM: arm/arm64: Move arm64-only vgic-v2-sr.c file to arm64
> KVM: arm/arm64: Handle VGICv3 save/restore from the main VGIC code on
> VHE
> KVM: arm/arm64: Move VGIC APR save/restore to vgic put/load
> KVM: arm/arm64: Avoid VGICv3 save/restore on VHE with no IRQs
>
> Shih-Wei Li (1):
> KVM: arm64: Move HCR_INT_OVERRIDE to default HCR_EL2 guest flag
>
> arch/arm/include/asm/kvm_asm.h | 5 +-
> arch/arm/include/asm/kvm_emulate.h | 21 +-
> arch/arm/include/asm/kvm_host.h | 6 +-
> arch/arm/include/asm/kvm_hyp.h | 4 +
> arch/arm/kvm/emulate.c | 4 +-
> arch/arm/kvm/hyp/Makefile | 1 -
> arch/arm/kvm/hyp/switch.c | 16 +-
> arch/arm64/include/asm/kvm_arm.h | 4 +-
> arch/arm64/include/asm/kvm_asm.h | 18 +-
> arch/arm64/include/asm/kvm_emulate.h | 74 +++-
> arch/arm64/include/asm/kvm_host.h | 49 ++-
> arch/arm64/include/asm/kvm_hyp.h | 32 +-
> arch/arm64/include/asm/kvm_mmu.h | 2 +-
> arch/arm64/kernel/asm-offsets.c | 2 +
> arch/arm64/kvm/debug.c | 28 +-
> arch/arm64/kvm/guest.c | 3 -
> arch/arm64/kvm/hyp/Makefile | 2 +-
> arch/arm64/kvm/hyp/debug-sr.c | 88 +++--
> arch/arm64/kvm/hyp/entry.S | 9 +-
> arch/arm64/kvm/hyp/hyp-entry.S | 41 +--
> arch/arm64/kvm/hyp/switch.c | 404 +++++++++++++---------
> arch/arm64/kvm/hyp/sysreg-sr.c | 192 ++++++++--
> {virt/kvm/arm => arch/arm64/kvm}/hyp/vgic-v2-sr.c | 81 -----
> arch/arm64/kvm/inject_fault.c | 24 +-
> arch/arm64/kvm/regmap.c | 65 +++-
> arch/arm64/kvm/sys_regs.c | 247 +++++++++++--
> arch/arm64/kvm/sys_regs.h | 4 +-
> arch/arm64/kvm/sys_regs_generic_v8.c | 4 +-
> include/kvm/arm_vgic.h | 2 -
> virt/kvm/arm/aarch32.c | 2 +-
> virt/kvm/arm/arch_timer.c | 7 -
> virt/kvm/arm/arm.c | 50 ++-
> virt/kvm/arm/hyp/timer-sr.c | 44 +--
> virt/kvm/arm/hyp/vgic-v3-sr.c | 244 +++++++------
> virt/kvm/arm/mmu.c | 6 +-
> virt/kvm/arm/pmu.c | 37 +-
> virt/kvm/arm/vgic/vgic-init.c | 11 -
> virt/kvm/arm/vgic/vgic-v2.c | 61 +++-
> virt/kvm/arm/vgic/vgic-v3.c | 12 +-
> virt/kvm/arm/vgic/vgic.c | 21 ++
> virt/kvm/arm/vgic/vgic.h | 3 +
> 41 files changed, 1229 insertions(+), 701 deletions(-)
> rename {virt/kvm/arm => arch/arm64/kvm}/hyp/vgic-v2-sr.c (50%)
>
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