git: emx: Don't update TDT upon very packets transmitted

[Sepherosa Ziehau <sephe@xxxxxxxxxxxxxxxxxxxxxxx>]

commit 7f32a9b0f8f25e43ab2ae4ee0d82ce69325d3b4b
Author: Sepherosa Ziehau <sephe@dragonflybsd.org>
Date:   Thu Nov 22 20:53:36 2012 +0800

    emx: Don't update TDT upon very packets transmitted
    
    The TDT is updated only after certain amount of TX descriptors are
    added to the hardware TX ring.  The default value of the amount of
    TX descriptors are 8.  This value could be further tuned by per-device
    sysctl node hw.emxX.tx_wreg_nsegs.
    
    CPU usage when transmitting 18bytes tiny UDP datagrams @1.48Mpps with
    82571 on AMD970 (3500Mhz) are reduced from 50% to 30% with the default
    value.
    
    Inspired-by: FreeBSD netmap's paper

Summary of changes:
 sys/dev/netif/emx/if_emx.c |   51 +++++++++++++++++++++++++++++++++++++-------
 sys/dev/netif/emx/if_emx.h |    2 +
 2 files changed, 45 insertions(+), 8 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/7f32a9b0f8f25e43ab2ae4ee0d82ce69325d3b4b


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