Re: [PATCH] net: allow configuration of the size of page in __netdev_alloc_frag

On Wed, 2012-10-24 at 17:22 +0100, Ian Campbell wrote:

On Wed, 2012-10-24 at 16:21 +0100, Eric Dumazet wrote:

quoted

If you really have such problems, why locally generated TCP traffic
doesnt also have it ?

I think it does. The reason I noticed the original problem was that ssh
to the machine was virtually (no pun intended) unusable.

quoted

Your patch doesnt touch sk_page_frag_refill(), does it ?

That's right. It doesn't. When is (sk->sk_allocation & __GFP_WAIT) true?
Is it possible I'm just not hitting that case?

I hope not. GFP_KERNEL has __GFP_WAIT.

Is it possible that this only affects certain traffic patterns (I only
really tried ssh/scp and ping)? Or perhaps its just that the swiotlb is
only broken in one corner case and not the other.

Could you try a netperf -t TCP_STREAM ?

Because ssh use small packets, and small TCP packets dont use frags but
skb->head.

You mentioned a 70% drop of performance, but what test have you used
exactly ?