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Since irq_work is used for deferred MSR handling, >>>> any atomic console printing when entering cpuidle states can lead >>>> to the affected hardware hanging. Tegra20 and Tegra30 are examples >>>> of such platforms. Avoiding raising the irq_work IRQ has shown to >>>> circumvent the problem. >>> >>> I would argue that this is done for the benefit of less interrupts since >>> there no need to handle console_msr_work immediately. With the side >>> effect that it might fix a bug that was not yet reported on Tegra[23]0. >>> >>> Ideally the Tegra folks should figure out what exactly is broken instead >>> of adding duct tape everywhere else. >> >> Yes that would be ideal. Unfortunately these are old devices now and very >> much in maintenance mode so getting to the bottom of this now is unlikely. > > So this is maintenance mode. > >> You may say then why don't we completely deprecate these, but then you >> could argue the other way and say they have been working fine up until >> now. > > So a couple of years ago this platform stalled printk development due > its irq_work usage. Now again. Imagine we would have a ext4 feature > which freezes just this platform on boot. What would happen here? I simply reported a regression. I did not set out to stall any work. If the work stalled because of this issue alone, why was this not discussed back when this happened? I am sure we could have come to a reasonable comprise. Please note that these legacy boards have caught some other issues in the past and so I do see some value in keeping them working. This one is a bit of an odd ball because clearly this platform has some issues related to CPU idle. Again we are happy to discuss that and come to a reasonable comprise. > The current workaround is to use LAZY which in general defers the IRQ > work to the next tick and it works for you. If you enable NOHZ and the > CPU goes tickless even a scheduled LAZY irq-work will raise the irq-work > interrupt to ensure the CPU does not go idle and we do have a wake up. > > This might bring the problem back at some point. That may be, and we will cross that bridge if and when we come to it. Jon -- nvpublic