<div class="gmail_quote">On Tue, Nov 29, 2011 at 19:42, Ben Widawsky <<a href="mailto:ben@bwidawsk.net">ben@bwidawsk.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"> <div class="im">On Tue, Nov 29, 2011 at 01:01:31PM +0000, Chris Wilson wrote: > On Tue, 29 Nov 2011 10:55:04 -0200, Eugeni Dodonov <<a href="mailto:eugeni.dodonov@intel.com">eugeni.dodonov@intel.com</a>> wrote: > > This should allow even more energy saving when GPU is not in use. > > According to the testing, this state results in around 0.1 - 0.4 W better > > power usage. > > > > No issues or regressions observed so far, but additional testing is > > certainly welcome. > > The docs I saw said "not implemented; do not use". Do we have it on good > authority that this is safe and useful to enable? And doesn't it > require programming of more transition thresholds? > -Chris </div>Yes, I think we do have to program more stuff to make this work. Perhaps the BIOS puts in decent values for these registers though? We would have to restore those on reset and resume I'd guess. If BIOS doesn't use anything there, you probably aren't even entering these states. Also, for posterity, there are 3 rc6 states, rc6, deep rc6, and deepest rc6. I think deepest rc6 was recommended to avoid (though I don't recall a specific root caused issue, just some data from Jesse, from the windows team that it didn't seem stable). And I think deepest rc6 is also referred to as rc7 sometimes. </blockquote><div> We already setup the variables for both deep and deepest rc6 in our driver (GEN6_RC6p_* and GEN6_RC6pp_*), but we weren't using this additional state previously - if I understood the documentation and the code correctly, we do enable plain rc6 and deep rc6 currently. I haven't found any indications which would tell to avoid it in the latest docs, and I also haven't seen any regressions or issues with it being enabled on any of the machines, so I thought it would be worth trying that additional state as well. From the testing which QA did for this patch, looks like we save between 0.1 and 0.4W when compared to what we had with i915_enable_rc6=1. </div></div> But in any case, this is all highly experimental and I'll do more testing with it :). -- Eugeni Dodonov<a href="http://eugeni.dodonov.net/" target="_blank"> </a>