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Date: Thu, 04 Oct 2012 09:54:01 +0930 From: Rusty Russell <rusty@...tcorp.com.au> To: "Michael S. Tsirkin" <mst@...hat.com>, Thomas Lendacky <tahm@...ux.vnet.ibm.com> Cc: Sasha Levin <levinsasha928@...il.com>, virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH 2/3] virtio-net: correct capacity math on ring full "Michael S. Tsirkin" <mst@...hat.com> 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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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