* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 26 Aug 2009 16:40:09 -0400 (EDT) > Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx> wrote: > > > Peter has not given a solution to the problem. Nor have you. > > What problem? > > All I've seen is "I want 100% access to a CPU". That's not a problem > statement - it's an implementation. > > What is the problem statement? > > My take on these patches: the kernel gives userspace unmediated > access to memory resources if it wants that. The kernel gives > userspace unmediated access to IO devices if it wants that. But > for some reason people freak out at the thought of providing > unmediated access to CPU resources. Claiming all user-available CPU time from user-space is already possible: use SCHED_FIFO - the only question are remaining latencies in the final 0.01% of CPU time you cannot claim via SCHED_FIFO. ( Btw., this scheduling feature was implemented in Linux well before raw IO block devices were implemented, so i'm not sure what you mean by 'freaking out'. ) What we are objecting to are these easy isolation side-hacks for the remaining 0.01% that fail to address the real problem: the latencies. Those latencies can hurt not just isolated apps but _non isolated_ (and latency critical) apps too, and what we insist on is getting the proper fixes, not just ugly workarounds that side-step the problem. ( a secondary objection is the extension and extra layering of something that could be done within existing APIs/ABIs too. We want to minimize the configuration space. ) > Don't get all religious about this. If the change is clean, > maintainable and useful then there's no reason to not merge it. Precisely. This feature as proposed here hinders the correct solution being implemented - and hence hurts long term maintainability and hence is a no-merge right now. [It also weakens the pressure to fix latencies for a much wider set of applications, hence hurts the quality of Linux in the long run. (i.e. is a net step backwards)] Ingo -- 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
