Re: [RFC PATCH v4 net-next 1/4] tcp: replace cnt & rtt with struct in pkts_acked()

On 7/27/15, 11:46 AM, "Stephen Hemminger" [off-list ref]
wrote:

On Fri, 24 Jul 2015 19:47:03 -0700
Lawrence Brakmo [off-list ref] wrote:

quoted

Replace 2 arguments (cnt and rtt) in the congestion control modules'
pkts_acked() function with a struct. This will allow adding more
information without having to modify existing congestion control
modules (tcp_nv in particular needs bytes in flight when packet
was sent).

As proposed by Neal Cardwell in his comments to the tcp_nv patch.

Adding a layer of indirection makes code changes easier, but makes
the code slower. Arguments are passed in registers, and putting an
additional level of indirection only matters if you can't change
all the CC modules. Since this is the kernel and API compatability
doesn't matter, just pass more arguments.

I prefer the cleanliness of passing a structure and don¹t think the
overhead will be significant enough to worry about it.
Will the compiler pass struct values in registers if the struct is
passed by value?

I will be happy to do it either way (I did it like Stephen proposes
originally). What does everyone else think?

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