[crossbow-discuss] Re: [clearview-discuss] Re: softmac performance

[Nicolas Droux]

Cathy Zhou wrote:

>> Note that we are planning to revisit the GLDv3 locking as part of 
>> Crossbow.
>>
> Is this targgeted to improve performance?

The main goal is to accomodate the new data paths needed for Crossbow, 
as well as simplifying the locking architecture.

>> During the design review last year I also had a comment on the 
>> possible negative performance impact on having only one DL_PROMISC_SAP 
>> stream, which would disable the optimization that most DLPI drivers 
>> implement by saving a pointer to the IPv4 and IPv6 streams. This issue 
>> was not addressed by the design back then, and I don't know if it was 
>> looked at again as part of the softmac performance work.
>>
> I think the DL_PROMISC_SAP might disable the optimization of the 
> underlying driver, but it is not the main issue here:
> 
> On the recieve-side, the code path is roughly:
> 
> legacy_device_rput()->putnext()->softmac_rput()->mac_rx()->i_dls_link_rx()->ip_input(). 
> 
> 
> By removing all locks, loops in mac_rx() and i_dls_link_rx(), the 
> performance can improve from %-8 to %-0.9
> 
> Disabling the ipq_fastpath in legacy device might contribute to that 
> %0.9, but there is bigger issue than that.

What is not clear to me is why you seem to be focusing on the GLDv3 code 
path when you are disabling a common optimization done by existing DLPI 
drivers. It seems that doing an analysis of the lack of that 
optimization and its performance impact would be a useful step to take 
before revisiting the GLDv3 code path.

Nicolas.

> 
> Thanks
> - Cathy

-- 
Nicolas Droux, Solaris Kernel Networking
Sun Microsystems, Inc. http://blogs.sun.com/droux