Messages in this thread | | | Subject | RE: userspace irq balancer | Date | Fri, 23 May 2003 18:10:57 -0700 | From | "Nakajima, Jun" <> |
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> So, I suppose an argument could be made for setting the TPR to the vector > number on entry of do_IRQ. I don't think that would be a good idea.
I agree. If we start spl-like ranking of interrupts, we need to modify disable/enable_irq(), etc. as well, causing possible impacts to device derivers.
One thing that might be helpful here is to have 4-level of priorities, for example: Idle (0) User (0x10) Kernel (0x20) Interrupt (0x30)
Jun
> -----Original Message----- > From: James Cleverdon [mailto:jamesclv@us.ibm.com] > Sent: Thursday, May 22, 2003 8:30 AM > To: William Lee Irwin III > Cc: Gerrit Huizenga; Nakajima, Jun; haveblue@us.ibm.com; > pbadari@us.ibm.com; linux-kernel@vger.kernel.org; johnstul@us.ibm.com; > mannthey@us.ibm.com; Andrew Theurer > Subject: Re: userspace irq balancer > > On Thursday 22 May 2003 07:43 am, William Lee Irwin III wrote: > > On Thu, May 22, 2003 at 07:18:06AM -0700, James Cleverdon wrote: > > > Here's my old very stupid TPR patch . It lacks TPRing soft ints for > > > kernel preemption, etc. Because the xTPR logic only compares the top > > > nibble of the TPR and I don't want to mask out IRQs unnecessarily, it > > > only tracks busy/idle and IRQ/no-IRQ. > > > Simple enough for you, Bill? 8^) > > > > Simple enough, yes. But I hesitate to endorse it without making sure > > it's not too simple. > > > > It's much closer to the right direction, which is actually following > > hardware docs and then punting the fancy (potentially more performant) > > bits up into userspace. When properly tuned, it should actually have a > > useful interaction with explicit irq balancing via retargeting IO-APIC > > RTE destinations as interrupts targeted at a destination specifying > > multiple cpus won't always target a single cpu when TPR's are adjusted. > > > > The only real issue with the TPR is that it's an spl-like ranking of > > interrupts, assuming a static prioritization based on vector number. > > That doesn't really agree with the Linux model and is undesirable in > > various scenarios; however, it's how the hardware works and so can't > > be avoided (and the disastrous attempt to avoid it didn't DTRT anyway). > > > > > > -- wli > > Serial APICs have always had a spl-like effect built into them. The > effective > TPR value of a given local APIC is: > max(TPR, highest vector currently in progress) & 0xF0 > Parallel APICs don't do that because they don't have serial priority > arbitration; instead they use the xTPRs in the bridge chips. > > So, I suppose an argument could be made for setting the TPR to the vector > number on entry of do_IRQ. I don't think that would be a good idea. It > could interfere with IRQ nesting during a non-DMA IDE interrupt handler. > And > of course, an IRQ's vector has little to do with the IRQ itself, thanks to > the vector hashing scheme used to avoid the (stupid) 2 latches per APIC > level > HW limitation of most i586 and i686 CPUs. > > > -- > James Cleverdon > IBM xSeries Linux Solutions > {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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