Re: [PATCH 4/4] virtio_ring: unify direct/indirect code paths.

[Peter Zijlstra]

On Thu, May 29, 2014 at 04:56:45PM +0930, Rusty Russell wrote:
> virtqueue_add() populates the virtqueue descriptor table from the sgs
> given.  If it uses an indirect descriptor table, then it puts a single
> descriptor in the descriptor table pointing to the kmalloc'ed indirect
> table where the sg is populated.
> 
> Previously vring_add_indirect() did the allocation and the simple
> linear layout.  We replace that with alloc_indirect() which allocates
> the indirect table then chains it like the normal descriptor table so
> we can reuse the core logic.
> 
> Before:
> 	gcc 4.8.2: virtio_blk: stack used = 392
> 	gcc 4.6.4: virtio_blk: stack used = 480
> 
> After:
> 	gcc 4.8.2: virtio_blk: stack used = 408
> 	gcc 4.6.4: virtio_blk: stack used = 432

Is it worth it to make the good compiler worse? People are going to use
the newer GCC more as time goes on anyhow.

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