On Fri, 2009-02-27 at 05:14 -0700, Matthew Wilcox wrote: > On Thu, Feb 26, 2009 at 11:15:25PM -0700, Grant Grundler wrote: > > ... > > > +3. Why use MSIs? > > > + > > > +There are three reasons why using MSIs can give an advantage over > > > +traditional pin-based interrupts. > > ... > > > +PCI devices can only support a single pin-based interrupt per function. > > > > Related to this is a 4th reason: distribute workload across CPUs > > and enables construction of efficient, multi-queue devices. > > Care to mention that? > > That's true for MSI-X, but not for MSIs in general. Workload is already > distributed across CPUs with round-robin interrupts. I'm inclined to > leave out this level of detail. > > > > +The MSI-X capability is much more flexible than the MSI capability. > > > +It supports up to 2048 interrupts, each of which can be separately > > > +assigned. > > > > Nothing describes "assignment" below or what is meant by "assigned". > > My guess is you wanted to differentiate MSIX from MSI with: > > ... and each MSIX can be directed at a different CPU. So might each MSI, depending on the hardware. > > > +5.4. Finding why MSIs are disabled on a device > > > + > > > +From the above three sections, you can see that there are many reasons > > > +why MSIs may not be enabled for a given device. Your first step should > > > +be to examine your dmesg carefully to determine whether MSIs are enabled > > > +for your machine. You should also check your .config to be sure you > > > +have enabled CONFIG_PCI_MSI. > > > > Should mention "fgrep MSI /proc/interrupts" to see if any devices have > > MSI in use? > > Yes, you're right. That won't work on (some) powerpc machines at least .. because MSIs just get routed into the regular PIC. cheers -- Michael Ellerman OzLabs, IBM Australia Development Lab wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person
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