From: Alexander Duyck <aduyck@mirantis.com>
Date: Wed, 2 Mar 2016 21:16:01 +0000 (-0500)
Subject: e1000: Do not overestimate descriptor counts in Tx pre-check
X-Git-Tag: v4.1.12-105.0.20170622_2100~134
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=64f524b65fefe160983ab4618f08253b6fd07380;p=users%2Fjedix%2Flinux-maple.git

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>

Orabug: 26243014
(cherry picked from commit 847a1d6796c767f8b697ead60997b847a84b897b)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>
Reviewed-by: Ethan Zhao <ethan.zhao@oracle.com>
---

diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index e93acdfd5c06..7e568f8b7ee6 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -3111,7 +3111,7 @@ 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)
 {