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From: Marc Zyngier <marc.zyngier@arm.com>
To: Zenghui Yu <yuzenghui@huawei.com>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: "Raslan, KarimAllah" <karahmed@amazon.de>,
	"Saidi, Ali" <alisaidi@amazon.com>
Subject: Re: [PATCH v2 7/9] KVM: arm/arm64: vgic-its: Cache successful MSI->LPI translation
Date: Tue, 25 Jun 2019 13:31:36 +0100
Message-ID: <169cc847-ebfa-44b6-00e7-c69dccdbbd62@arm.com> (raw)
In-Reply-To: <53de88e9-3550-bd7f-8266-35c5e75fae4e@huawei.com>

Hi Zenghui,

On 25/06/2019 12:50, Zenghui Yu wrote:
> Hi Marc,
> 
> On 2019/6/12 1:03, Marc Zyngier wrote:
>> On a successful translation, preserve the parameters in the LPI
>> translation cache. Each translation is reusing the last slot
>> in the list, naturally evincting the least recently used entry.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>   virt/kvm/arm/vgic/vgic-its.c | 86 ++++++++++++++++++++++++++++++++++++
>>   1 file changed, 86 insertions(+)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 0aa0cbbc3af6..62932458476a 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -546,6 +546,90 @@ static unsigned long vgic_mmio_read_its_idregs(struct kvm *kvm,
>>   	return 0;
>>   }
>>   
>> +static struct vgic_irq *__vgic_its_check_cache(struct vgic_dist *dist,
>> +					       phys_addr_t db,
>> +					       u32 devid, u32 eventid)
>> +{
>> +	struct vgic_translation_cache_entry *cte;
>> +	struct vgic_irq *irq = NULL;
>> +
>> +	list_for_each_entry(cte, &dist->lpi_translation_cache, entry) {
>> +		/*
>> +		 * If we hit a NULL entry, there is nothing after this
>> +		 * point.
>> +		 */
>> +		if (!cte->irq)
>> +			break;
>> +
>> +		if (cte->db == db &&
>> +		    cte->devid == devid &&
>> +		    cte->eventid == eventid) {
>> +			/*
>> +			 * Move this entry to the head, as it is the
>> +			 * most recently used.
>> +			 */
>> +			list_move(&cte->entry, &dist->lpi_translation_cache);
> 
> Only for performance reasons: if we hit at the "head" of the list, we
> don't need to do a list_move().
> In our tests, we found that a single list_move() takes nearly (sometimes
> even more than) one microsecond, for some unknown reason...

Huh... That's odd.

Can you narrow down under which conditions this happens? I'm not sure if
checking for the list head would be more efficient, as you end-up
fetching the head anyway. Can you try replacing this line with:

	if (!list_is_first(&cte->entry, &dist->lpi_translation_cache))
		list_move(&cte->entry, &dist->lpi_translation_cache);

and let me know whether it helps?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-11 17:03 [PATCH v2 0/9] KVM: arm/arm64: vgic: ITS translation cache Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 1/9] KVM: arm/arm64: vgic: Add LPI translation cache definition Marc Zyngier
2019-06-12  8:16   ` Julien Thierry
2019-06-12  8:49     ` Julien Thierry
2019-06-12  9:52     ` Marc Zyngier
2019-06-12 10:58       ` Julien Thierry
2019-06-12 12:28         ` Julien Thierry
2019-07-23 12:43   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 2/9] KVM: arm/arm64: vgic: Add __vgic_put_lpi_locked primitive Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 3/9] KVM: arm/arm64: vgic-its: Add MSI-LPI translation cache invalidation Marc Zyngier
2019-07-23 12:39   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 4/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on specific commands Marc Zyngier
2019-07-01 12:38   ` Auger Eric
2019-07-22 10:54     ` Marc Zyngier
2019-07-23 12:25       ` Auger Eric
2019-07-23 12:43         ` Marc Zyngier
2019-07-23 12:47           ` Auger Eric
2019-07-23 12:50             ` Marc Zyngier
2019-06-11 17:03 ` [PATCH v2 5/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on disabling LPIs Marc Zyngier
2019-07-23 15:09   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 6/9] KVM: arm/arm64: vgic-its: Invalidate MSI-LPI translation cache on vgic teardown Marc Zyngier
2019-07-23 15:10   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 7/9] KVM: arm/arm64: vgic-its: Cache successful MSI->LPI translation Marc Zyngier
2019-06-25 11:50   ` Zenghui Yu
2019-06-25 12:31     ` Marc Zyngier [this message]
2019-06-25 16:00       ` Zenghui Yu
2019-06-26  3:54         ` Zenghui Yu
2019-06-26  7:55         ` Marc Zyngier
2019-07-23 15:21   ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 8/9] KVM: arm/arm64: vgic-its: Check the LPI translation cache on MSI injection Marc Zyngier
2019-07-23 15:10   ` Auger Eric
2019-07-23 15:45     ` Marc Zyngier
2019-07-24  7:41       ` Auger Eric
2019-06-11 17:03 ` [PATCH v2 9/9] KVM: arm/arm64: vgic-irqfd: Implement kvm_arch_set_irq_inatomic Marc Zyngier
2019-07-23 15:14   ` Auger Eric
2019-07-25  8:24     ` Marc Zyngier
2019-07-23 11:14 ` [PATCH v2 0/9] KVM: arm/arm64: vgic: ITS translation cache Andre Przywara
2019-07-25  8:50   ` Marc Zyngier
2019-07-25 10:01     ` Andre Przywara
2019-07-25 15:37       ` Marc Zyngier

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