Comment # 26
on bug 111482
from Andrew Sheldon
(In reply to Eduardo from comment #25) > I have a PowerColor RedDevil 5700XT and for me, Kernel 5.4-rc1 just works. > Memory clocks always at 100Mhz when idle, even using KDE (Plasma 5.16). > I'm using Display Port, with FreeSync ON, on a 75HZ monitor, with 2560x1080 > resolution. It works for you because your resolution is below a certain threshold in resolution and refresh rate, and not a multi-monitor setup. Anyway, I think I have a clearer picture of things now. Firstly, Navi does still have a few additional power consumption issues (as compared to Vega). One such issue is that if during the boot sequence the monitor switches to 144hz (the default on one of my monitors), than that's it, it's impossible to clock down from the maximum mclk at any point. One workaround is to boot with the monitor unplugged, then plug it in after. It seems to happen later in the boot sequence (but before X) so it's possible this can be worked around by changing framebuffer settings. Furthermore, 2560x1440@144hz in general forces the card to the maximum clock (even with the workaround, although you can switch down to a different mode at least), whereas Vega stays at a lower mclk. Secondly, multi-monitor configurations will force the card to the maximum clock, by design (on all GPUs). You can workaround this by setting both cards to the same resolution/refresh rate, provided you have a newer kernel. However, this doesn't work with Navi. Another hacky workaround is to write data to the powerplay tables while in dual-monitor setup with mismatched modes, but this is just a hack, and I can't promise stability (although it worked for me, again, only with Vega). Thirdly, Navi uses a lot more power at idle compared to Vega, even when both are in the maximum mclk. E.g. Vega uses around 15W, in a multi-monitor configuration (2560x1440@90 + 2560x1440@144). Whereas Navi will use 36W for pretty much any configuration that hits the maximum mclk. It could be that HBM is more efficient, lower voltages, or even a reporting error (I haven't tested at the wall, yet). So in short: - Navi + 144hz at boot completely breaks mclk switching - Navi + 144hz uses unnecessarily high mclk (compared to Vega) - Multi-monitor high mclk is by design (all GPUs) - Navi uses a lot more power at idle than Vega, when at the same mclk
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