On Tue, Nov 22, 2011 at 12:46 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Tue, 2011-11-22 at 00:18 +0100, John Kacur wrote: > >> Imagine you have a uni-processor system and want to do real-time. >> According to the descriptions in init/Kconfig, you would want to >> select TINY_PREEMPT_RCU. The description is >> >> This option selects the RCU implementation that is designed >> for real-time UP systems. This option greatly reduces the >> memory footprint of RCU. >> >> Without this patch, you cannot choose this option because of the && >> !PREEMPT_RT_FULL >> So, that is a bug, and makes this patch appropriate for stable. > > > 3.0-rt never supported rcutiny, which means adding it now is not a bug > fix but a new feature. Sure, it may have been a mistake that Thomas kept > rcutiny out for 3.0-rt, but because 3.0-rt never supported it, and > 3.0-rt can fully support rcutree with !SMP, there is no bug to be fixed > here. You're adding a new feature to stable, not fixing someones > problem. > >> >> I suppose if you want to be really conservative, you can say we only >> need that third hunk. >> However, this upstream patch, makes these options in v3.0-rt match the >> options in v3.2-rc2-rt3. >> >> Furthermore, it doesn't seem like a good idea to me to support >> configurations in a stable branch that are not supported upstream. > > No, upstream changed the game, in which the configuration can't be > supported. But the stable release can fully support this configuration. > there's no reason to this change just because the latest tree can't > support it. It's like we have to deprecate everything in stable that has > been deprecated in upstream. > > Stable is not a mirror of upstream, it's a snapshot in time. Only if we > discover something that crashes, or causes huge latencies do we want to > update stable. Not when we realized that a feature wasn't supported by > -rt. > Okay, I get that and I agree with you - will try to be more careful about that in the future. However, in this particular case, I don't think there is a viable rcu choice for UP real-time. Perhaps we can revisit this again in the future if anyone cares about it. Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
