Messages in this thread | | | Date | Mon, 15 Nov 2010 17:47:54 -0800 | From | Stepan Moskovchenko <> | Subject | Re: [PATCH 09/14] msm: iommu: Kconfig option for cacheable page tables |
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On 11/15/2010 10:20 AM, Daniel Walker wrote: > 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
Alright. Fixed in v2.
Steve
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