e1000: Do not overestimate descriptor counts in Tx pre-check

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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>

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Alexander Duyck 2016-03-02 16:16:01 -05:00 • committed by Jeff Kirsher

parent 8e2cc0e67f

commit 847a1d6796

1 changed files with 1 additions and 1 deletions

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drivers/net/ethernet/intel/e1000/e1000_main.c

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