netdev - Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

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Message-ID: <540996A9.4060100@redhat.com>
Date:	Fri, 05 Sep 2014 12:55:37 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	netdev <netdev@...r.kernel.org>
CC:	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH 3/3] virtio_ring: unify direct/indirect code paths.

Il 03/09/2014 06:29, Rusty Russell ha scritto:
> + 	desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
> + 	if (!desc)
> +		return NULL;
>  
> -	return head;
> +	for (i = 0; i < total_sg; i++)
> +		desc[i].next = i+1;
> +	return desc;
>  }

Would it make sense to keep a cache of a few (say) 8- or 16-element
indirect descriptors?  You'd only have to do this ugly (and slowish) for
loop on the first allocation.

Also, since this is mostly an aesthetic patch,

> +	if (indirect)
> +		vq->free_head = vq->vring.desc[head].next;
> +	else
> +		vq->free_head = i;

I'd move the indirect case above, where the vring.desc[head] is actually
allocated.

Paolo
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