linux-kernel - Re: [PATCH] drivers/virtio/virtio_ring.c: Deinline virtqueue

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Date:	Sat, 9 Apr 2016 23:14:37 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/virtio/virtio_ring.c: Deinline virtqueue_add,
 save 1016 bytes

On Fri, Apr 08, 2016 at 08:58:44PM +0200, Denys Vlasenko wrote:
> This function compiles to 839 bytes of machine code.
> In C, it is ~150 lines long.
> 
> This function has 3 callsites.
> 
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: "Michael S. Tsirkin" <mst@...hat.com>
> CC: virtualization@...ts.linux-foundation.org
> CC: linux-kernel@...r.kernel.org

This function is one of the most performance critical ones in the driver, a
bunch of tuning went into it, making this inline intentionally.  I'd
have to see some numbers showing making it non-inline is a worth-while
tradeoff.

> ---
>  drivers/virtio/virtio_ring.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index e12e385..77a4771 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -126,7 +126,7 @@ static struct vring_desc *alloc_indirect(struct virtqueue *_vq,
>  	return desc;
>  }
>  
> -static inline int virtqueue_add(struct virtqueue *_vq,
> +static int virtqueue_add(struct virtqueue *_vq,
>  				struct scatterlist *sgs[],
>  				unsigned int total_sg,
>  				unsigned int out_sgs,
> -- 
> 2.1.0