Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs copies out

Johannes Berg
2013-02-20T16:20:43Z

On Wed, 2013-02-20 at 07:11 -0800, Eric Dumazet wrote:
> On Wed, 2013-02-20 at 10:15 +0100, Johannes Berg wrote:
>
> > OTOH, this affects the protocol, and when you really can't allocate any
> > order-1 pages you pointed out yourself that many other things also won't
> > work, so I'm not really sure it makes a big difference if we change the
> > driver?
>
> It will make a huge difference, even on non pressure mode, as TCP
> receive window will grow twice faster.

Hmm, why does that depend on the allocation size?

> Unless wifi speed reaches 10Gbps, following patch should do the trick
>
>
> diff --git a/drivers/net/wireless/iwlwifi/dvm/rx.c b/drivers/net/wireless/iwlwifi/dvm/rx.c
> index a4eed20..77a3ee3 100644
> --- a/drivers/net/wireless/iwlwifi/dvm/rx.c
> +++ b/drivers/net/wireless/iwlwifi/dvm/rx.c
> @@ -750,7 +750,12 @@ static void iwlagn_pass_packet_to_mac80211(struct iwl_priv *priv,
> /* Dont use dev_alloc_skb(), we'll have enough headroom once
> * ieee80211_hdr pulled.
> */
> - skb = alloc_skb(128, GFP_ATOMIC);
> + fraglen = 128;
> + /* if we use order-1 pages, copy to get better TCP performance */
> + if (rxb->truesize > PAGE_SIZE)
> + fraglen = max_t(unsigned, fraglen, len);
> +
> + skb = alloc_skb(fraglen, GFP_ATOMIC);

Hmm, I don't quite understand -- that's not doing any copy?

FWIW if you do the copy you should not "steal" the pages, then they'd be
recycled in the RX ring right away.

johannes

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