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SubjectRe: 2.6.12-rc5-mm2: "bic unavailable using TCP reno" messages
On Thu, Jun 02, 2005 at 10:38:05AM -0700, Stephen Hemminger wrote:
> On Thu, 02 Jun 2005 14:58:17 +0100
> Baruch Even <> wrote:
> >...
> Your right, the sysctl handler should be smarter, but that is not the problem here.
> The problem is that the default value is set to be BIC to be compatible with earlier kernels.
> Since 75% of the world isn't smart enough to figure out how to use sysctl, there is a
> question of what the default should be, and what to do if that is missing.
> One version had a messy ifdef chain to try and avoid the warning:
> char sysctl_tcp_congestion_control[] =
> #if defined(CONFIG_TCP_BIC)
> "bic"
> #elif defined(CONFIG_TCP_HTCP)
> "htcp"
> #else
> "reno"
> #endif
> ;
> but that was ugly.
> Another possibility is putting it in as yet another config value at kernel build time.

One thing that currently makes all solutions harder (and the #ifdef
example above not ugly but simply wrong) is that you allow modular
congestion control options for the always static net support.

Is this really required?

The IO schedulers have a similar problem, and they are using the #ifdef
approach for selecting the default.

One approach is to actually choose the default using #ifdef's.

You could also do any kind of runtime selection, but please don't print
the warning more than once.



"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed

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