Hi Lorenzo and Chander, On Wed, Jun 11, 2014 at 6:45 PM, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > On Wed, Jun 11, 2014 at 01:14:21PM +0100, Chander Kashyap wrote: >> On Wed, Jun 11, 2014 at 3:43 PM, Lorenzo Pieralisi >> <lorenzo.pieralisi@xxxxxxx> wrote: >> > On Wed, Jun 11, 2014 at 05:52:10AM +0100, Chander Kashyap wrote: >> >> Hi Doug, >> >> >> >> On Tue, Jun 10, 2014 at 9:19 PM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote: >> >> > On Tue, 10 Jun 2014, Doug Anderson wrote: >> >> > >> >> >> My S-state knowledge is not strong, but I believe that Lorenzo's >> >> >> questions matter if we're using S2 for CPUidle (where we actually turn >> >> >> off power and hot unplug CPUs) but not when we're using S1 for CPUidle >> >> >> (where we just enter WFI/WFE). >> >> >> >> >> >> >> No Its not plain WFI. >> >> >> >> All cores in Exynos5420 can be powered off independently. >> >> This functionality has been tested. >> >> >> >> Below is the link for the posted patches. >> >> >> >> https://lkml.org/lkml/2014/6/10/194 >> >> >> >> And as Nicolas wrote, these patches need MCPM for that. >> > >> > Chander, I cast a look into the code and I have a question >> > (you also told me on CPUidle review that only core off >> > is supported in CPUidle). >> > >> > When you say all cores can be powered off independently, do >> > you also mean that clusters can be powered off (in CPUidle) ? >> > >> > I am pointing this out since in the MCPM backend I noticed: >> > >> > "/* TODO: Turn off the cluster here to save power. */" This is something that pends on me. >> > >> > I do not see any cluster power down request in the down path. >> > >> > If I am wrong, ignore my message, I am just writing to help. >> > >> > If you can only power down cores, but not the clusters on idle, >> > please keep in mind that you are currently cleaning and invalidating >> > the L2 when last man is running and this must not be taken >> > lightly since, if L2 stays on, that's a massive energy waste >> > for nothing. >> > >> > So, if clusters stay up, you _have_ to tweak the MCPM backend slightly >> > to avoid cleaning L2, that's pivotal. >> >> Hi Lorenzo, >> Cluster shutdown is in progress. Abhilash will add support for that. >> >> https://www.mail-archive.com/linux-samsung-soc@xxxxxxxxxxxxxxx/msg31104.html > > Hi Chander, > > thanks. So, as a heads-up: > > 1) if you merge CPUidle support now, as it is it is at least suboptimal, may > even burn more energy than it saves. Latencies in the bL idle driver > are likely to be wrong, since they are for cluster shutdown and for > TC2, not core power gating that should require shorter target_residencies. > On top of that, L2 is cleaned and invalidated for nothing. > 2) when cluster support is merged, you might want to extend the CPUidle > driver to add an additional state (ie C1 core gating, C2 cluster > gating) and to do that you should extend the driver and the MCPM > back-end accordingly, I discussed that with Nico already some time ago > and actually it should be fairly easy to do but we have got to talk > about that. I have already implemented the missing cluster power down code and tested it on an exynos5420 based chromebook. I plan to post the patch as soon as I am back in office, which should be early next week. Regards, Abhilash > > Thank you, > Lorenzo > >> >> >> > >> > Lorenzo >> > >> >> >> >> >> I believe that in ChromeOS we use S1 CPUidle and that it works fine. >> >> >> We've never implemented S2 that I'm aware of. >> >> > >> >> > You'll have to rely on MCPM for that. That's probably why it hasn't >> >> > been implemented before. >> >> > >> >> > >> >> > Nicolas >> >> > >> >> > _______________________________________________ >> >> > linux-arm-kernel mailing list >> >> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> >> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >> >> -- >> >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> Please read the FAQ at http://www.tux.org/lkml/ >> >> >> > >> > -- >> > To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in >> > the body of a message to majordomo@xxxxxxxxxxxxxxx >> > More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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