git: bge: Improve tiny packets transmission performance on low frequency CPU

[Sepherosa Ziehau <sephe@xxxxxxxxxxxxxxxxxxxxxxx>]

commit aad8b3fefb192f89783f0b1e383f701aafd4f00b
Author: Sepherosa Ziehau <sephe@dragonflybsd.org>
Date:   Sun Dec 2 20:30:40 2012 +0800

    bge: Improve tiny packets transmission performance on low frequency CPU
    
    Update TX HOST_PROD register a little bit often; mainly to improve
    timeliness of packets transmission:
    The TX HOST_PROD register is updated after certain amount of TX
    descriptors are added to the hardware TX ring.  The default value of the
    amount of TX descriptors are 16.  This value could be further tuned by
    per-device sysctl node hw.bgeX.tx_wreg.
    
    The default value improves tiny packets transmission performance w/ 5721
    on AMD970@800Mhz (770Kpps -> 800Kpps) and it does not increase CPU usage
    on AMD970@3500Mhz (CPU usage stays @20%, 5721 could only do 810Kpps).
    
    NOTE: Tuning hw.bgeX.tx_coal_bds to 32 could make packets transmission
    performance w/ 5721 on AMD970@800Mhz to be 810Kpps, however, this shows
    no performance improvement on commonly used CPU frequency like 2200Mhz
    and 3500Mhz.  And this tuning could burden systems not using polling(4).

Summary of changes:
 sys/dev/netif/bge/if_bge.c    |   58 ++++++++++++++++++++++++++--------------
 sys/dev/netif/bge/if_bgevar.h |    1 +
 2 files changed, 39 insertions(+), 20 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/aad8b3fefb192f89783f0b1e383f701aafd4f00b


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