On Tue, Apr 25, 2006 at 07:29:40AM -0400, linux-os (Dick Johnson) wrote: > >> Message signaled interrupts are just a kudge to save a trace on a > >> PC board (read make junk cheaper still). > > > > yes. Also in PCI-Express there is no physical interrupt line anymore due to > > the architecture, so even classical interrupts are sent as "message" over > > the bus. > > > >> They are not faster and may even be slower. > > > > thus in the case of PCI-Express, MSI interrupts are just as fast as the > > ordinary ones. I have no numbers on whether MSI is faster or not then e.g. > > interrupts on PCI-X, but generally speaking, the PCI-Express bus is not > > designed to be "low latency" at all, at best it gives you X latency, where X > > is something like microseconds. The MSI message itself only takes 10-20 > > nanoseconds though, but all the handling probably adds a large factor to > > that > > (1000 or so). No clue on classical interrupt line latency - anyone? > > About 9 nanosecond per foot of FR-4 (G10) trace, plus the access time > through the gate-arrays (about 20 ns) so, from the time a device needs > the CPU, until it hits the interrupt pin, you have typically 30 to > 50 nanoseconds. Of course the CPU is __much__ slower. However, these > physical latencies are in series, cannot be compensated for because > the CPU can't see into the future. You seem to be missing the fact that most of todays interrupts are delivered through the APIC bus, which isn't fast at all.
-- Vojtech Pavlik Director SuSE Labs - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
