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Re: [PATCH v4 2/4] xen/arm: optimize the size of struct vcpu
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Mon, 29 Dec 2025 12:10:15 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, "Volodymyr Babchuk" <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Mon, 29 Dec 2025 11:10:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29/12/2025 12:08, Orzel, Michal wrote:
>
>
> On 23/12/2025 18:01, Oleksii Kurochko wrote:
>> When CONFIG_NEW_VGIC=y and CONFIG_ARM_64=y, the size of struct vcpu
>> exceeds one page, which requires allocating two pages and led to the
>> introduction of MAX_PAGES_PER_VCPU.
Also, I think it would be better to drop MAX_PAGES_PER_VCPU in this patch.
~Michal
>>
>> To remove the need for MAX_PAGES_PER_VCPU in a follow-up patch, the vgic
>> member of NEW_VGIC's struct vgic_vcpu member private_irq is changed to a
> s/vgic_vcpu/vgic_cpu/
> s/private_irq/private_irqs/
>
>> pointer to struct vgic_irq.
>> As a result, the size of struct vcpu for Arm64 is reduced to 2176 bytes,
>> compared to 3840 bytes (without these changes and with CONFIG_ARM_64=y)
>> and 4736 bytes (without these changes and with both CONFIG_ARM_64=y and
>> CONFIG_NEW_VGIC=y).
> You only touch new vGIC, so there should be no size reduction without it but
> the
> paragraph reads as if the change affected both old and new vGIC. Also I would
> mention that probably you provided the numbers based on a defconfig target.
>
>>
>> Since the private_irqs member is now a pointer, vcpu_vgic_init() and
>> vcpu_vgic_free() are updated to allocate and free private_irqs instance.
>>
>> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
>> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Other than that:
> Acked-by: Michal Orzel <michal.orzel@xxxxxxx>
>
> ~Michal
>
>
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