Messages in this thread | | | Date | Fri, 29 Jan 2010 12:41:38 -0600 | From | Joel Schopp <> | Subject | Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt_power for Power7 |
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Benjamin Herrenschmidt wrote: > On Thu, 2010-01-28 at 17:24 -0600, Joel Schopp wrote: > >> On Power7 processors running in SMT4 mode with 2, 3, or 4 idle threads >> there is performance benefit to idling the higher numbered threads in >> the core. >> >> This patch implements arch_scale_smt_power to dynamically update smt >> thread power in these idle cases in order to prefer threads 0,1 over >> threads 2,3 within a core. >> > > Almost there :-) Joel, Peter, can you help me figure something out tho ? > > On machine that don't have SMT, I would like to avoid calling > arch_scale_smt_power() at all if possible (in addition to not compiling > it in if SMT is not enabled in .config). > > Now, I must say I'm utterly confused by how the domains are setup and I > haven't quite managed to sort it out... it looks to me that > SD_SHARE_CPUPOWER is always going to be set on all CPUs when the config > option is set (though each CPU will have its own domain) or am I > misguided ? IE. Is there any sense in having at least a fast exit path > out of arch_scale_smt_power() for non-SMT CPUs ? > > Joel, can you look at compiling it out when SMT is not set ? We don't > want to bloat SMP kernels for 32-bit non-SMT embedded platforms. > I can wrap the powerpc definition of arch_scale_smt in an #ifdef, if it's not there the scheduler uses the default, which is the same as it uses if SMT isn't compiled.
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