"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> Capacity math on ring full is wrong: we are
> looking at num_sg but that might be optimistic
> because of indirect buffer use.
>
> The implementation also penalizes fast path
> with extra memory accesses for the benefit of
> ring full condition handling which is slow path.
>
> It's easy to query ring capacity so let's do just that.
This path will reduce the actual queue use to worst-case assumptions.
With bufferbloat maybe that's a good thing, but it's true.
If we do this, the code is now wrong:
/* This can happen with OOM and indirect buffers. */
if (unlikely(capacity < 0)) {
Because this should now *never* happen.
But I do like the cleanup; returning capacity from add_buf() was always
hacky. I've got an idea, we'll see what it looks like...
Cheers,
Rusty.
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