On Sun, 2010-11-14 at 18:56 -0800, Stepan Moskovchenko wrote: > > On Fri, 2010-11-12 at 19:29 -0800, Stepan Moskovchenko wrote: > >> > >> +config IOMMU_PGTABLES_L2 > >> + depends on ARCH_MSM8X60 > >> + depends on MMU > >> + depends on CPU_DCACHE_DISABLE=n > >> + depends on SMP > >> + bool "Cacheable IOMMU page tables" > >> + default y > >> + help > >> + Allows the IOMMU page tables to be brought into the L2 cache. This > >> + improves the TLB miss latency at the expense of potential pollution > >> + of the L2 cache. This option has been shown to improve multimedia > >> + performance in some cases. > >> + > >> + If unsure, say Y here. > > > > Why would someone want this off? > > > > The other thing is that you usually want this included with the code > > that uses the option. > > The code that uses it had gone in during a previous patch series, but I > didn't want to meddle in the Kconfig just yet, especially since the option > only improves performance and does not add new functionality at a high > level. This patch should be the last of what is needed for this feature. > > You would want to turn this off if you wanted more deterministic behavior > from the multimedia subsystem, such as when trying to run benchmarks for > the worst-case behavior in terms of memory latency and TLB misses. You > might also want to turn it off if you are debugging memory problems that > you suspect might be related to the cache maintenance code, in which case > turning this off would give an idea as to whether that is the problem. > Similarly, this needs to be off (and will be, due to the dependencies) if > certain required things (like the Dcache, MMU, etc) have been disabled. > Finally, if you are doing things with the MMSS that you know will not > result in many TLB misses, (or if you know that you can tolerate high miss > latency) you may as well turn this off to avoid the (small) bit of cache > pollution. It sounds like you don't really want it off unless your a developer (or you turn one of the dependencies) .. I think this might be better as a hidden option just cause of the developer centric nature of it. Daniel -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
