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>
847a1d6796