Nicolas Pitre wrote: > On Fri, 26 Mar 2010, Peter Zijlstra wrote: > > > On Fri, 2010-03-26 at 09:59 +0000, Alan Cox wrote: > > > > As long as it's rare (which it is) i dont see a problem: you can enable > > > > interrupts in the handler by using local_irq_enable(), like the IDE PIO > > > > drivers do. That way it's documented a bit better as well, because it shows > > > > the precise source of the latency, with a big comment explaining it, etc. > > > > > > I don't think it's as rare as you think particularly in embedded, and the > > > moment you start explicitly using local_irq_enable() you've simply moved > > > the underlying problem back and made it far harder to grep for. > > > > We've got local_irq_enable_in_hardirq() which should be used and can > > easily be grep'ed for. > > > > But yes, I would much prefer to simply convert these known slow handlers > > to threaded interrupts. > > Can't do that. The smc91x has a very small internal buffer which has to > be emptied using PIO. Threaded interrupts simply have too high > latencies for overruns not to occur. That's why the RX path is entirely > done in hardirq context while the TX path is done in softirq context. Although I wouldn't be surprised to find threaded interrupts are too slow on certain hardware, is that _fundamental_ to threaded interrupts, or is it just that our implementation doesn't have the funky hot path straight direct from hardirq -> running high priority RT irq thread when it exceeds previously running priority? In other words, can we swizzle threaded irqs into something more resembling software-implemented hard irq priorities, while cunningly updating the kernel state just enough to look like it's a thread? -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
