Messages in this thread | | | Subject | Re: [PATCH RT] ehea: make receive irq handler non-threaded (IRQF_NODELAY) | From | Jan-Bernd Themann <> | Date | Mon, 20 Sep 2010 16:26:22 +0200 |
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Hi Milton,
sorry for the delayed answer, was on vacation.
linux-kernel-owner@vger.kernel.org wrote on 21.05.2010 11:18:01: > linux-kernel-owner@vger.kernel.org > > On Thu, 20 May 2010 at 10:21:36 +0200 (CEST) Thomas Gleixner wrote: > > On Thu, 20 May 2010, Michael Ellerman wrote: > > > On Wed, 2010-05-19 at 16:38 +0200, Thomas Gleixner wrote: > > > > On Wed, 19 May 2010, Darren Hart wrote: > > > > > > > > > On 05/18/2010 06:25 PM, Michael Ellerman wrote: > > > > > > On Tue, 2010-05-18 at 15:22 -0700, Darren Hart wrote: > > > > > > > > > The result of the discussion about two years ago on this was that we > > > > > > needed a custom flow handler for XICS on RT. > > > > > > > > > > I'm still not clear on why the ultimate solution wasn't to > have XICS report > > > > > edge triggered as edge triggered. Probably some complexity > of the entire power > > > > > stack that I am ignorant of. > > > > > > > > > > > Apart from the issue of loosing interrupts there is also > the fact that > > > > > > masking on the XICS requires an RTAS call which takes a global lock. > > > > > > > > Right, I'd love to avoid that but with real level interrupts we'd run > > > > into an interrupt storm. Though another solution would be to issue the > > > > EOI after the threaded handler finished, that'd work as well, but > > > > needs testing. > > > > > > Yeah I think that was the idea for the custom flow handler. We'd reset > > > the processor priority so we can take other interrupts (which the EOI > > > usually does for you), then do the actual EOI after the handler > > > finished. > > > > That only works when the card does not issue new interrupts until the > > EOI happens. If the EOI is only relevant for the interrupt controller, > > then you are going to lose any edge which comes in before the EOI as > > well. > > Well, the real MSIs have an extra bit to allow the eoi to dally behind > the mmio on another path and that should cover this race when the irq > is left enabled. > > Jan-Bernd HEA has that change, right?
I don't now. We never hit problems so we did not look very deep into this area. We probably have to talk to the HEA HW developers to be sure.
Regards, Jan-Bernd
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