On 3/24/22 07:10, Linus Torvalds wrote: > On Mon, Mar 21, 2022 at 11:57 PM Damien Le Moal > <damien.lemoal@xxxxxxxxxxxxxxxxxx> wrote: >> >> * Rename ahci_board_mobile to board_ahci_low_power to be more descriptive >> of the feature as that is also used on PC and server AHCI adapters, >> from Mario. >> >> Mario Limonciello (3): >> ata: ahci: Rename board_ahci_mobile >> ata: ahci: Rename `AHCI_HFLAG_IS_MOBILE` >> ata: ahci: Rename CONFIG_SATA_LPM_MOBILE_POLICY configuration item > > So I've pulled this, but it's worth noting that particularly renaming > that CONFIG option was probably not a good idea. > > Why? > > Because it means that people silently lose their old values. And it has that > > range 0 4 > default 0 > > with 4 being explicitly marked as very dangerous - but at least Fedora > seems to actually have a default of 3 in their kernels: > > /boot/config-5.16.13-200.fc35.x86_64: > CONFIG_SATA_MOBILE_LPM_POLICY=3 > > so that "default 0" may actually not be the right one. Yes. Mario has follow up patches to change the default. But as changing it may break things, we are going to try it early this cycle so that it can get lots of linux-next testing. Since Fedora has had the default of 3 for a long time now, changing the kernel default from 0 to 3 should be OK. The goal here is of course to have a default kernel config that is more eco-friendly. > Now, we're at the point where few enough people likely care about ATA, > but the corollary to that is also that these kinds of changes can > cause user pain that then developers have *no* idea about. > Particularly when the pain ends up being caused by some subtle default > config option silently changing that nobody even thought about. > > Now, that "default 0" is probably the only safe default - and I don't > dispute that part. But I also suspect that Fedora chose that value '3' > because it probably makes a noticeable power use difference on at > least some platforms. Most laptops benefit from it. And yes, most laptop today have switched to NVMe, but there are still a fair amount out there using SATA SSDs and 2.5" HDDs, even new ones (low end models). > I don't know. But I doubt really *anybody* knows, so renaming them and > silently likely changing config options for some less-than-critical > reason is just not a great idea. Understood. I will monitor this and see if a revert of the rename is needed. For now, I do prefer the new name as it reflects the fact that link power management policies are not for mobile chipsets anymore and also apply to regular server chipsets where power consumption really matters too. -- Damien Le Moal Western Digital Research
