| Message ID | 20160302211601.2124.64160.stgit@localhost.localdomain |
|---|---|
| State | Awaiting Upstream, archived |
| Delegated to: | David Miller |
| Headers | show |
> From: netdev-owner@vger.kernel.org [mailto:netdev- > owner@vger.kernel.org] On Behalf Of Alexander Duyck > Sent: Wednesday, March 2, 2016 1:16 PM > To: netdev@vger.kernel.org; jogreene@redhat.com; intel-wired- > lan@lists.osuosl.org; Kirsher, Jeffrey T <jeffrey.t.kirsher@intel.com>; > sassmann@redhat.com > Subject: [net PATCH 1/2] 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> > --- > drivers/net/ethernet/intel/e1000/e1000_main.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Tested-by: Aaron Brown <aaron.f.brown@intel.com>
diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c index 3fc7bde..d213fb4 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) {
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> --- drivers/net/ethernet/intel/e1000/e1000_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)