Luc Perneel wrote: > On Jan 15, 2008 2:58 AM, Thiemo Seufer <ths@xxxxxxxxxxxx> wrote: > > > The Engineer wrote: > > > We are working with a 2.6.12 kernel on a dual-core mips architecture. > > > In this dual-core system, one core is running the linux kernel and the > > > other is used for some real-time handling (not directly controlled by > > > Linux) > > > We had different stability issues, which could be pinpointed to be > > > related with cache aliasing problems. > > > Cache aliasing happens when the same physical memory can be cached > > > twice as it is accessed by two different virtual addresses. > > > Indeed, for the index to select the correct cache line the virtual > > > address is used. If some bits of the virtual page address are used in > > > the cache index, aliasing can occur. > > > > > > > > > As there is no hardware solution in the mips to recover from this > > > (which would provide some cache coherency, even for one core), the > > > only intrinsic safe solution is to enlarge the page size, so that > > > cache indexing is only done by the offset address in the page (thus > > > the physical part of the address). > > > Another solution is to flush the cache if a page is being remapped to > > > an aliased address (but in our case linux does not has control on the > > > second core, which can cause issues with shared data between both > > > cores). > > > Currently the second solution is used in the kernel, but we found > > > different issues with it (for instance: we had to merge more recent > > > mips kernels, to get a reliable copy-on-write behaviour after > > > forks...). > > > > > > Therefore some questions: > > > - Are there still some known issues with cache aliasing in the MIPS > > kernel? > > > - Are there known issues when using 16KB pages (8KB pages seems not be > > > possible due to tlb issues). > > > > With recent kernels and toolchains 16k pages work ok IME. With a 2.6.12 > > kernel however you'll have to backport a serious amount of bugfixes > > before 16k pages can work. Upgrading the kernel is probably less work. > > > > Thiemo > > > Thanks for the info, any idea from which kernel this works ok? I believe the linux-2.6.22-stable branch from www.linux-mips.org is the best version to use. I don't recall if the earlier branches got all the necessary fixes. Thiemo
