From: Zenghui Yu <yuzenghui@huawei.com>
To: Marc Zyngier <maz@kernel.org>
Cc: <kvmarm@lists.cs.columbia.edu>, <linux-kernel@vger.kernel.org>,
Eric Auger <eric.auger@redhat.com>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jason Cooper <jason@lakedaemon.net>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Andrew Murray <andrew.murray@arm.com>,
Jayachandran C <jnair@marvell.com>,
Robert Richter <rrichter@marvell.com>
Subject: Re: [PATCH v2 13/36] irqchip/gic-v4.1: Don't use the VPE proxy if RVPEID is set
Date: Thu, 19 Dec 2019 11:05:09 +0800 [thread overview]
Message-ID: <aba3b852-9ab9-c3b6-f19d-2bc18bd6566a@huawei.com> (raw)
In-Reply-To: <762f78e917ac501629729fcf7718178c@www.loen.fr>
Hi Marc,
On 2019/12/18 22:39, Marc Zyngier wrote:
> On 2019-11-01 11:05, Zenghui Yu wrote:
>> Hi Marc,
>>
>> On 2019/10/27 22:42, Marc Zyngier wrote:
>>> The infamous VPE proxy device isn't used with GICv4.1 because:
>>> - we can invalidate any LPI from the DirectLPI MMIO interface
>>> - the ITS and redistributors understand the life cycle of
>>> the doorbell, so we don't need to enable/disable it all
>>> the time
>>> So let's escape early from the proxy related functions.
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>
>> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
>>
>>> ---
>>> drivers/irqchip/irq-gic-v3-its.c | 23 ++++++++++++++++++++++-
>>> 1 file changed, 22 insertions(+), 1 deletion(-)
>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c
>>> b/drivers/irqchip/irq-gic-v3-its.c
>>> index 220d490d516e..999e61a9b2c3 100644
>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>> @@ -3069,7 +3069,7 @@ static const struct irq_domain_ops
>>> its_domain_ops = {
>>> /*
>>> * This is insane.
>>> *
>>> - * If a GICv4 doesn't implement Direct LPIs (which is extremely
>>> + * If a GICv4.0 doesn't implement Direct LPIs (which is extremely
>>> * likely), the only way to perform an invalidate is to use a fake
>>> * device to issue an INV command, implying that the LPI has first
>>> * been mapped to some event on that device. Since this is not exactly
>>> @@ -3077,9 +3077,18 @@ static const struct irq_domain_ops
>>> its_domain_ops = {
>>> * only issue an UNMAP if we're short on available slots.
>>> *
>>> * Broken by design(tm).
>>> + *
>>> + * GICv4.1 actually mandates that we're able to invalidate by
>>> writing to a
>>> + * MMIO register. It doesn't implement the whole of DirectLPI, but
>>> that's
>>> + * good enough. And most of the time, we don't even have to invalidate
>>> + * anything, so that's actually pretty good!
>>
>> I can't understand the meaning of this last sentence. May I ask for an
>> explanation? :)
>
> Yeah, reading this now, it feels pretty clumsy, and only remotely
> connected to the patch.
>
> What I'm trying to say here is that, although GICv4.1 doesn't have
> the full spectrum of v4.0 DirectLPI (it only allows a subset of it),
> this subset is more then enough for us. Here's the rational:
>
> When a vPE exits from the hypervisor, we know whether we need to
> request a doorbell or not (depending on whether we're blocking on
> WFI or not). On GICv4.0, this translates into enabling the doorbell
> interrupt, which generates an invalidation (costly). And whenever
> we've taken a doorbell, or are scheduled again, we need to turn
> the doorbell off (invalidation again).
>
> With v4.1, we can just say *at exit time* whether we want doorbells
> to be subsequently generated (see its_vpe_4_1_deschedule() and the
> req_db parameter in the info structure). This is part of making
> the vPE non-resident, so we have 0 overhead at this stage.
Great, and get it. Thanks for this clear explanation!
Zenghui
next prev parent reply other threads:[~2019-12-19 3:05 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-27 14:41 [PATCH v2 00/36] irqchip/gic-v4: GICv4.1 architecture support Marc Zyngier
2019-10-27 14:41 ` [PATCH v2 01/36] KVM: arm64: vgic-v4: Move the GICv4 residency flow to be driven by vcpu_load/put Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 02/36] irqchip/gic-v3-its: Factor out wait_for_syncr primitive Marc Zyngier
2019-10-28 9:20 ` Zenghui Yu
2019-11-20 13:21 ` [tip: irq/core] " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 03/36] irqchip/gic-v3-its: Allow LPI invalidation via the DirectLPI interface Marc Zyngier
2019-10-31 8:49 ` Zenghui Yu
2019-11-01 13:26 ` Marc Zyngier
2019-11-05 10:30 ` Zenghui Yu
2019-11-05 12:12 ` Marc Zyngier
2019-11-20 13:21 ` [tip: irq/core] " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 04/36] irqchip/gic-v3-its: Make is_v4 use a TYPER copy Marc Zyngier
2019-10-28 9:34 ` Zenghui Yu
2019-10-28 10:52 ` Marc Zyngier
2019-11-20 13:21 ` [tip: irq/core] " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 05/36] irqchip/gic-v3-its: Kill its->ite_size and use TYPER copy instead Marc Zyngier
2019-10-28 9:40 ` Zenghui Yu
2019-11-20 13:21 ` [tip: irq/core] " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 06/36] irqchip/gic-v3-its: Kill its->device_ids " Marc Zyngier
2019-10-31 6:33 ` Zenghui Yu
2019-10-31 8:30 ` Marc Zyngier
2019-10-31 9:08 ` Zenghui Yu
2019-11-20 13:21 ` [tip: irq/core] " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 07/36] irqchip/gic-v3-its: Add get_vlpi_map() helper Marc Zyngier
2019-10-31 3:54 ` Zenghui Yu
2019-11-20 13:21 ` [tip: irq/core] irqchip/gic-v3-its: Add its_vlpi_map helpers tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 08/36] irqchip/gic-v3: Detect GICv4.1 supporting RVPEID Marc Zyngier
2019-10-31 11:34 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 09/36] irqchip/gic-v3: Add GICv4.1 VPEID size discovery Marc Zyngier
2019-10-31 12:02 ` Zenghui Yu
2019-11-01 15:13 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 10/36] irqchip/gic-v3: Workaround Cavium TX1 erratum when reading GICD_TYPER2 Marc Zyngier
2020-03-15 9:55 ` [tip: irq/urgent] irqchip/gic-v3: Workaround Cavium erratum 38539 " tip-bot2 for Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 11/36] irqchip/gic-v4.1: VPE table (aka GICR_VPROPBASER) allocation Marc Zyngier
2019-12-24 7:10 ` Zenghui Yu
2019-12-24 9:19 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 12/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMAPP Marc Zyngier
2019-11-01 10:58 ` Zenghui Yu
2019-11-13 8:02 ` Zenghui Yu
2019-11-13 9:47 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 13/36] irqchip/gic-v4.1: Don't use the VPE proxy if RVPEID is set Marc Zyngier
2019-11-01 11:05 ` Zenghui Yu
2019-12-18 14:39 ` Marc Zyngier
2019-12-19 3:05 ` Zenghui Yu [this message]
2019-10-27 14:42 ` [PATCH v2 14/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMOVP Marc Zyngier
2019-11-01 11:10 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 15/36] irqchip/gic-v4.1: Plumb skeletal VPE irqchip Marc Zyngier
2019-11-01 11:13 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 16/36] irqchip/gic-v4.1: Add mask/unmask doorbell callbacks Marc Zyngier
2019-11-01 11:23 ` Zenghui Yu
2019-12-18 15:06 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 17/36] irqchip/gic-v4.1: Add VPE residency callback Marc Zyngier
2019-11-01 11:34 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 18/36] irqchip/gic-v4.1: Add VPE eviction callback Marc Zyngier
2019-11-01 11:39 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 19/36] irqchip/gic-v4.1: Add VPE INVALL callback Marc Zyngier
2019-11-01 11:51 ` Zenghui Yu
2019-12-18 14:18 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 20/36] irqchip/gic-v4.1: Suppress per-VLPI doorbell Marc Zyngier
2019-11-01 12:17 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 21/36] irqchip/gic-v4.1: Allow direct invalidation of VLPIs Marc Zyngier
2019-11-01 12:30 ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 22/36] irqchip/gic-v4.1: Advertise support v4.1 to KVM Marc Zyngier
2019-11-01 12:55 ` Zenghui Yu
2019-12-18 14:48 ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 23/36] irqchip/gic-v4.1: Map the ITS SGIR register page Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 24/36] irqchip/gic-v4.1: Plumb skeletal VSGI irqchip Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 25/36] irqchip/gic-v4.1: Add initial SGI configuration Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 26/36] irqchip/gic-v4.1: Plumb mask/unmask SGI callbacks Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 27/36] irqchip/gic-v4.1: Plumb get/set_irqchip_state " Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 28/36] irqchip/gic-v4.1: Plumb set_vcpu_affinity " Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 29/36] irqchip/gic-v4.1: Move doorbell management to the GICv4 abstraction layer Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 30/36] irqchip/gic-v4.1: Add VSGI allocation/teardown Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 31/36] irqchip/gic-v4.1: Add VSGI property setup Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 32/36] irqchip/gic-v4.1: Eagerly vmap vPEs Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 33/36] KVM: arm64: GICv4.1: Let doorbells be auto-enabled Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 34/36] KVM: arm64: GICv4.1: Add direct injection capability to SGI registers Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 35/36] KVM: arm64: GICv4.1: Configure SGIs as HW interrupts Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 36/36] KVM: arm64: GICv4.1: Expose HW-based SGIs in debugfs Marc Zyngier
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