On Monday, May 20, 2013 07:34:44 AM Bjorn Helgaas wrote: > On Fri, May 17, 2013 at 7:20 PM, Phillip Susi <psusi@xxxxxxxxxx> wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA1 > > > > On 05/17/2013 08:40 PM, Bjorn Helgaas wrote: > >> Right; I meant RO per the PCIe spec. If it's RW on your chip, > >> setpci should be able to write it. > > > > I assume it would do no good to change it at this point; it would need > > to already be set at the time the kernel reads it and decides whether > > or not to enable it, so I'd have to have grub set it before loading > > the kernel. > > Yeah, setting the capability bits after the kernel has booted wouldn't > change anything except what lspci reports. > > >> If you can measure the power consumption, you might be able to see > >> a difference there. I've seen people report that, but don't know > >> how they do it. For example: > >> https://lkml.kernel.org/r/CANUX_P3F5YhbZX3WGU-j1AGpbXb_T9Bis2ErhvKkFMtDvzatVQ@xxxxxxxxxxxxxx > > > > After > >> > > enabling it on both ends ( despite the root port still claiming > > it is not supported ) I still see ~121 watts according to the > > Kill-A-Watt my system is plugged into. Oh well. > > ASPM only saves power when the PCIe link is idle. I'm not a video > person, so I don't know how video usage translates into link usage, > and I don't know how much power it saves. My guess is that the amount > is fairly small and might not be measurable with a Kill-A-Watt. I'm pretty sure it's measurable, at least in some cases. Phoronix did quite some fuss about a commit that caused ASPM to not work any more on some systems some time ago, so he had to be able to measure it (and it was called a "major power regression"). Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
