Pain

Posted Nov 22, 2013 4:42 UTC (Fri) by mjg59 (subscriber, #23239)
In reply to: Pain by ncm
Parent article: ACPI for ARM?

And I find the entire area of memory management and process scheduling to be unbearably painful, but I don't complain about NUMA being awful. Nobody in Linux-land was really paying attention to ACPI until hardware started shipping with it, and even after that we spent several years deciding to obsess over implementing the spec rather than reality. The increased involvement of Linux vendors in working groups makes it unlikely that anything similar will happen again, though we do need to come up with a compelling story for supporting Connected Standby.

The ARM case is somewhat different. Some vendors apparently want to use ACPI, but they won't tell us why (I heard nothing even when I was maintaining most of the RHEL ACPI code at Red Hat). There's an apparent disconnect between what vendors expect Linux to offer and what people are actually working on implementing. You're right that the end result might well be painful, but it's going to be painful for entirely different reasons.

Pain

Posted Nov 22, 2013 9:13 UTC (Fri) by cesarb (subscriber, #6266) [Link]

I'd guess that what the vendors want is "PCs with their x86 CPU removed and an ARM chip put in there". That is, common code (and probably common hardware) for both their x86 and their arm64 servers.

I'd thus also guess that the vendors pushing ACPI would be the same ones which already have x86 servers. The vendors with only ARM products would instead prefer DT.

Pain

Posted Nov 22, 2013 14:04 UTC (Fri) by jdulaney (subscriber, #83672) [Link] (4 responses)

For Linux to wait on Microsoft to set the standards is so amazingly short sighted as to be table-flipping stupid. It is quite obvious that arm64 servers are going to be using ACPI whether we like it or not, and to not implement support for them is basically telling Microsoft that they can just have the market; we'll get out of your way and roll out the read carpet, on, and here is the Scotch you ordered.

Pain

Posted Nov 22, 2013 15:57 UTC (Fri) by olof (subscriber, #11729) [Link] (2 responses)

If you read the thread instead of what Jon chose to pick out of it, you'll see that nobody is actually proposing that. I'm pushing the subject to get discussion going, which seems to have been successful. Too many people have been grumbling about this for quite a while now but nobody actually put a foot down -- it was time to do so to at least shake out technical motivations for ACPI (so far there have been zero, even after bringing it up).

We can't drop everything and spend significant efforts trying to figure out ACPI instead of making the first rounds of systems work well with the means we have at hand -- that's not going to help anybody besides the people betting against Linux on ARM servers.

If some people want to keep ACPI a possible alternative while we continue working on the platforms, that's perfectly fine, but we shouldn't let it become a distraction for everybody.

Pain

Posted Nov 22, 2013 16:07 UTC (Fri) by olof (subscriber, #11729) [Link]

(Clarification: s/proposing/serious about/)

Pain

Posted Nov 25, 2013 2:00 UTC (Mon) by marcH (subscriber, #57642) [Link]

> If you read the thread instead of what Jon chose to pick out of it,...

Unfortunately life is too short, which is why there is LWN.

Pain

Posted Nov 22, 2013 17:21 UTC (Fri) by mjg59 (subscriber, #23239) [Link]

That's… not what I said? If we don't know what the vendors want from ACPI then adding random support is utterly meaningless. If what they want from ACPI turns out to be incompatible with reality then that's going to be painful for everybody. It's important to know what the problems we're supposed to be solving actually are.