From 847a1d6796c767f8b697ead60997b847a84b897b Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Wed, 2 Mar 2016 16:16:01 -0500 Subject: [PATCH] e1000: Do not overestimate descriptor counts in Tx pre-check The current code path is capable of grossly overestimating the number of descriptors needed to transmit a new frame. This specifically occurs if the skb contains a number of 4K pages. The issue is that the logic for determining the descriptors needed is ((S) >> (X)) + 1. When X is 12 it means that we were indicating that we required 2 descriptors for each 4K page when we only needed one. This change corrects this by instead adding (1 << (X)) - 1 to the S value instead of adding 1 after the fact. This way we get an accurate descriptor needed count as we are essentially doing a DIV_ROUNDUP(). Reported-by: Ivan Suzdal Signed-off-by: Alexander Duyck Tested-by: Aaron Brown Signed-off-by: Jeff Kirsher --- drivers/net/ethernet/intel/e1000/e1000_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c index 3fc7bde699ba..d213fb45855d 100644 --- a/drivers/net/ethernet/intel/e1000/e1000_main.c +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c @@ -3106,7 +3106,7 @@ static int e1000_maybe_stop_tx(struct net_device *netdev, return __e1000_maybe_stop_tx(netdev, size); } -#define TXD_USE_COUNT(S, X) (((S) >> (X)) + 1) +#define TXD_USE_COUNT(S, X) (((S) + ((1 << (X)) - 1)) >> (X)) static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev) { -- 2.30.2