netdev - Re: [PATCH RFC 15/13] gpio: virtio: reorder fields to reduce struct padding

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Message-ID: <w6to6itartzrxgapaj6dys2q3yqqoz3zetpb5bejnjb4heof2c@jkhmal3chyn2>
Date: Mon, 5 Jan 2026 10:27:11 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>, 
	Jonathan Corbet <corbet@....net>, Olivia Mackall <olivia@...enic.com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Jason Wang <jasowang@...hat.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
	Eugenio Pérez <eperezma@...hat.com>, "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Gerd Hoffmann <kraxel@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Robin Murphy <robin.murphy@....com>, Stefano Garzarella <sgarzare@...hat.com>, 
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	Jason Gunthorpe <jgg@...pe.ca>, linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org, 
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org, iommu@...ts.linux.dev, 
	kvm@...r.kernel.org, netdev@...r.kernel.org, 
	"Enrico Weigelt, metux IT consult" <info@...ux.net>, Viresh Kumar <vireshk@...nel.org>, 
	Linus Walleij <linusw@...nel.org>, Bartosz Golaszewski <brgl@...nel.org>, 
	linux-gpio@...r.kernel.org
Subject: Re: [PATCH RFC 15/13] gpio: virtio: reorder fields to reduce struct
 padding

On 30-12-25, 11:40, Michael S. Tsirkin wrote:
> Reorder struct virtio_gpio_line fields to place the DMA buffers (req/res)
> last. This eliminates the need for __dma_from_device_aligned_end padding
> after the DMA buffer, since struct tail padding naturally protects it,
> making the struct a bit smaller.
> 
> Size reduction estimation when ARCH_DMA_MINALIGN=128:
> - request is 8 bytes
> - response is 2 bytes
> - removing _end saves up to 128-6=122 bytes padding to align rxlen field
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/gpio/gpio-virtio.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh