On Thu, Jan 19, 2012 at 1:21 PM, Stuart Yoder <b08...@gmail.com> wrote: > On Wed, Jan 18, 2012 at 3:10 PM, Benjamin Herrenschmidt > <b...@kernel.crashing.org> wrote: >> On Wed, 2012-01-18 at 16:35 +0200, Laurentiu Tudor wrote: >>> This patch adds a menuconfig option that allows controlling >>> the lazy interrupt disabling feature implemented by this >>> commit: >>> >>> commit d04c56f73c30a5e593202ecfcf25ed43d42363a2 >>> Author: Paul Mackerras >>> Date: Wed Oct 4 16:47:49 2006 +1000 >>> >>> [POWERPC] Lazy interrupt disabling for 64-bit machines >>> >>> The code in 'powerpc/include/asm/hw_irq.h' was rearranged and >>> cleaned-up a bit in order to reduce the number of needed #ifdef's. >> >> It's still nasty. Do you have numbers showing that it's worth disabling >> on BookE ? > > It's not just about bare metal performance-- some platforms such as > the Freescale > Topaz hypervisor don't provide legacy IACK type interrupt > acknowledgment, and expect > the guest to support the external proxy mechanism. > > With Topaz, interrupts go directly to guests and we don't want to require a > trap/hcall to do an IACK, as that adds potentially thousands of cycles of > latency to every interrupt. > > As you know, with external proxy interrupts are acknowledged by the > hardware and it becomes problematic to replay the interrupt in > the context of lazy EE when interrupts are re-enabled. The interrupt > will not fire again when you enable EE. > > That is currently the issue, as we can't run the 64-bit kernel on Topaz. > Our option are: > 1) to provide an option to disable lazy EE > 2) do some kind of hack to replay interrupts with lazy EE > 3) change Topaz to support legacy IACK, but this gets ugly for > various reasons. > > Providing a config option to disable lazy EE seemed to be a good > approach.
Also, Scott had posted an approach to do option #2 a while back, but as I recall there was some negative feedback about this. See: <http://lists.ozlabs.org/pipermail/linuxppc-dev/2011-August/092103.html> Stuart _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
