[PATCH] irqchip/gic-v4.1: Optimize the wait for the completion of the analysis of the VPT
Marc Zyngier
maz at kernel.org
Fri Nov 27 14:35:51 EST 2020
Shenming,
Somehow this patch ended up in the wrong folder.
Apologies for the delay reviewing it.
On 2020-09-23 07:35, Shenming Lu wrote:
> Right after a vPE is made resident, the code starts polling the
> GICR_VPENDBASER.Dirty bit until it becomes 0, where the delay_us
> is set to 10. But in our measurement, it takes only hundreds of
> nanoseconds, or 1~2 microseconds, to finish parsing the VPT in most
> cases. And we also measured the time from vcpu_load() (include it)
> to __guest_enter() on Kunpeng 920. On average, it takes 2.55
> microseconds
> (not first run && the VPT is empty). So 10 microseconds delay might
> really hurt performance.
>
> To avoid this, we can set the delay_us to 1, which is more appropriate
> in this situation and universal. Besides, we can delay the execution
> of its_wait_vpt_parse_complete() (call it from kvm_vgic_flush_hwstate()
> corresponding to vPE resident), giving the GIC a chance to work in
> parallel with the CPU on the entry path.
>
> Signed-off-by: Shenming Lu <lushenming at huawei.com>
> ---
> arch/arm64/kvm/vgic/vgic-v4.c | 18 ++++++++++++++++++
> arch/arm64/kvm/vgic/vgic.c | 2 ++
> drivers/irqchip/irq-gic-v3-its.c | 14 +++++++++++---
> drivers/irqchip/irq-gic-v4.c | 11 +++++++++++
> include/kvm/arm_vgic.h | 3 +++
> include/linux/irqchip/arm-gic-v4.h | 4 ++++
> 6 files changed, 49 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/vgic/vgic-v4.c
> b/arch/arm64/kvm/vgic/vgic-v4.c
> index b5fa73c9fd35..1d5d2d6894d3 100644
> --- a/arch/arm64/kvm/vgic/vgic-v4.c
> +++ b/arch/arm64/kvm/vgic/vgic-v4.c
> @@ -353,6 +353,24 @@ int vgic_v4_load(struct kvm_vcpu *vcpu)
> return err;
> }
>
> +void vgic_v4_wait_vpt(struct kvm_vcpu *vcpu)
I'd like something a bit more abstract as a name.
vgic_v4_commit() seems more appropriate, and could be used for other
purposes.
> +{
> + struct its_vpe *vpe;
> +
> + if (kvm_vgic_global_state.type == VGIC_V2 ||
Why do you test for GICv2? Isn't the vgic_supports_direct_msis() test
enough?
And the test should be moved to kvm_vgic_flush_hwstate(), as we already
have
similar checks there.
> !vgic_supports_direct_msis(vcpu->kvm))
> + return;
> +
> + vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> +
> + if (vpe->vpt_ready)
> + return;
> +
> + if (its_wait_vpt(vpe))
> + return;
How can that happen?
> +
> + vpe->vpt_ready = true;
This is nasty. You need to explain what happens with this state (you are
trying not to access VPENDBASER across a shallow exit, as only a
vcpu_put
will invalidate the GIC state). And something like vpe_ready is more
generic (we try not to have too much of the GICv4 gunk in the KVM code).
> +}
> +
> static struct vgic_its *vgic_get_its(struct kvm *kvm,
> struct kvm_kernel_irq_routing_entry *irq_entry)
> {
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index c3643b7f101b..ed810a80cda2 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -915,6 +915,8 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
>
> if (can_access_vgic_from_kernel())
> vgic_restore_state(vcpu);
> +
> + vgic_v4_wait_vpt(vcpu);
> }
>
> void kvm_vgic_load(struct kvm_vcpu *vcpu)
> diff --git a/drivers/irqchip/irq-gic-v3-its.c
> b/drivers/irqchip/irq-gic-v3-its.c
> index 548de7538632..b7cbc9bcab9d 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -3803,7 +3803,7 @@ static void its_wait_vpt_parse_complete(void)
> WARN_ON_ONCE(readq_relaxed_poll_timeout_atomic(vlpi_base +
> GICR_VPENDBASER,
> val,
> !(val & GICR_VPENDBASER_Dirty),
> - 10, 500));
> + 1, 500));
This really should be in a separate patch.
> }
>
> static void its_vpe_schedule(struct its_vpe *vpe)
> @@ -3837,7 +3837,7 @@ static void its_vpe_schedule(struct its_vpe *vpe)
> val |= GICR_VPENDBASER_Valid;
> gicr_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
>
> - its_wait_vpt_parse_complete();
> + vpe->vpt_ready = false;
This really belongs to the deschedule path, doesn't it? Given that
it can only be set from vgic_flush_hwstate(), it should be fairly
foolproof.
> }
>
> static void its_vpe_deschedule(struct its_vpe *vpe)
> @@ -3881,6 +3881,10 @@ static int its_vpe_set_vcpu_affinity(struct
> irq_data *d, void *vcpu_info)
> its_vpe_schedule(vpe);
> return 0;
>
> + case WAIT_VPT:
COMMIT_VPE seems a better name.
> + its_wait_vpt_parse_complete();
> + return 0;
> +
> case DESCHEDULE_VPE:
> its_vpe_deschedule(vpe);
> return 0;
> @@ -4047,7 +4051,7 @@ static void its_vpe_4_1_schedule(struct its_vpe
> *vpe,
>
> gicr_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
>
> - its_wait_vpt_parse_complete();
> + vpe->vpt_ready = false;
> }
>
> static void its_vpe_4_1_deschedule(struct its_vpe *vpe,
> @@ -4118,6 +4122,10 @@ static int its_vpe_4_1_set_vcpu_affinity(struct
> irq_data *d, void *vcpu_info)
> its_vpe_4_1_schedule(vpe, info);
> return 0;
>
> + case WAIT_VPT:
> + its_wait_vpt_parse_complete();
> + return 0;
> +
> case DESCHEDULE_VPE:
> its_vpe_4_1_deschedule(vpe, info);
> return 0;
> diff --git a/drivers/irqchip/irq-gic-v4.c
> b/drivers/irqchip/irq-gic-v4.c
> index 0c18714ae13e..36be42569872 100644
> --- a/drivers/irqchip/irq-gic-v4.c
> +++ b/drivers/irqchip/irq-gic-v4.c
> @@ -258,6 +258,17 @@ int its_make_vpe_resident(struct its_vpe *vpe,
> bool g0en, bool g1en)
> return ret;
> }
>
> +int its_wait_vpt(struct its_vpe *vpe)
its_commit_vpe()
> +{
> + struct its_cmd_info info = { };
> +
> + WARN_ON(preemptible());
> +
> + info.cmd_type = WAIT_VPT;
Please write it as:
struct its_cmd_info = {
.cmd_type = COMMIT_VPE,
};
as for most of the commands.
> +
> + return its_send_vpe_cmd(vpe, &info);
> +}
> +
> int its_invall_vpe(struct its_vpe *vpe)
> {
> struct its_cmd_info info = {
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index a8d8fdcd3723..b55a835d28a8 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -402,6 +402,9 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm,
> int irq,
> struct kvm_kernel_irq_routing_entry *irq_entry);
>
> int vgic_v4_load(struct kvm_vcpu *vcpu);
> +
> +void vgic_v4_wait_vpt(struct kvm_vcpu *vcpu);
> +
> int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db);
>
> #endif /* __KVM_ARM_VGIC_H */
> diff --git a/include/linux/irqchip/arm-gic-v4.h
> b/include/linux/irqchip/arm-gic-v4.h
> index 6976b8331b60..68ac2b7b9309 100644
> --- a/include/linux/irqchip/arm-gic-v4.h
> +++ b/include/linux/irqchip/arm-gic-v4.h
> @@ -75,6 +75,8 @@ struct its_vpe {
> u16 vpe_id;
> /* Pending VLPIs on schedule out? */
> bool pending_last;
> + /* VPT parse complete */
> + bool vpt_ready;
> };
>
> /*
> @@ -103,6 +105,7 @@ enum its_vcpu_info_cmd_type {
> PROP_UPDATE_VLPI,
> PROP_UPDATE_AND_INV_VLPI,
> SCHEDULE_VPE,
> + WAIT_VPT,
> DESCHEDULE_VPE,
> INVALL_VPE,
> PROP_UPDATE_VSGI,
> @@ -128,6 +131,7 @@ struct its_cmd_info {
> int its_alloc_vcpu_irqs(struct its_vm *vm);
> void its_free_vcpu_irqs(struct its_vm *vm);
> int its_make_vpe_resident(struct its_vpe *vpe, bool g0en, bool g1en);
> +int its_wait_vpt(struct its_vpe *vpe);
> int its_make_vpe_non_resident(struct its_vpe *vpe, bool db);
> int its_invall_vpe(struct its_vpe *vpe);
> int its_map_vlpi(int irq, struct its_vlpi_map *map);
My comments are mostly cosmetic. If you can respin quickly, I'll
pick it up for 5.11.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
More information about the linux-arm-kernel
mailing list