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

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Date:	Wed, 20 Feb 2013 07:11:04 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Marc MERLIN <marc@...lins.org>, David Miller <davem@...emloft.net>,
	Larry.Finger@...inger.net, bhutchings@...arflare.com,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs
 copies out

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.

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);
 	if (!skb) {
 		IWL_ERR(priv, "alloc_skb failed\n");
 		return;


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