On Wed, Sep 24, 2014 at 09:04:44AM -0400, Tejun Heo wrote: > Hello, Alexander. > > On Wed, Sep 24, 2014 at 11:42:15AM +0100, Alexander Gordeev wrote: > > On Tue, Sep 23, 2014 at 04:57:10PM -0400, Tejun Heo wrote: > > > Hmmm... how does it affect single device operation tho? It does make > > > individual interrupt handling heavier, no? > > > > I think it is difficult to assess "individual interrupt handling", since > > it depends from both the hardware and device access pattern. On the system > > I use the results are rather counter-intuitive: ahci_thread_fn() does not > > show up in perf report at all, nor ahci_single_irq_intr(). While before > > the change ahci_single_irq_intr() reported 0.00%. > > > > But since the handling is split in two parts it is rather incorrect to > > apply the same metric to the threaded context. Obviously, the threaded > > handler is expected slowed down by other interrupts handlers, but the > > whole system should benefit from it, which is exactly the aim of this > > change. > > Hmmm, how would the whole system benefit from it if there's only > single device? Each individual servicing of the interrupt does more > now which includes scheduling which may end up adding to completion > latency. As Chuck noticed, non-AHCI hardware context handlers will benefit. > The thing I don't get is why multiple MSI handling and this patchset > are tied to threaded interrupt handling. Multiple MSIs were implemented with the above aim (let's say aim #1) right away. Single MSI/IRQ handling is getting updated with this series. > Splitting locks don't > necessarily have much to do with threaded handling and it's not like > ahci interrupt handling is heavy. The hot path is pretty short > actually. The meat of the work - completing requests and propagating > completions - is offloaded to softirq by block layer anyway. So the aim (let's say aim #2) is to avoid any of those to compete with hardware context handler. IOW, not to wait on host/port spinlocks with local interrupts disabled unnecessarily. I assume, if at the time of writing of original handlers the two interrupt context existed, they were written the way I propose now :) > Just to be clear, I'm not against the proposed changes but wanna > understand the justifications behind them. Should I send the fixed series? ;) > Thanks. > > -- > tejun -- Regards, Alexander Gordeev agordeev@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
