path: root/drivers/net/ethernet/intel/e1000
diff options
authorAlexander Duyck <aduyck@mirantis.com>2016-03-02 16:16:01 -0500
committerJeff Kirsher <jeffrey.t.kirsher@intel.com>2016-04-05 14:59:05 -0700
commit847a1d6796c767f8b697ead60997b847a84b897b (patch)
tree3fdd2c06bf101b77ed307ef0fd2625eb4fef39dc /drivers/net/ethernet/intel/e1000
parenti40e: fix errant PCIe bandwidth message (diff)
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 <isuzdal@mirantis.com> Signed-off-by: Alexander Duyck <aduyck@mirantis.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Diffstat (limited to 'drivers/net/ethernet/intel/e1000')
1 files changed, 1 insertions, 1 deletions
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)