Trading off safety and performance in the kernel

Posted May 13, 2015 21:31 UTC (Wed) by javispedro (guest, #83660)
In reply to: Trading off safety and performance in the kernel by zblaxell
Parent article: Trading off safety and performance in the kernel

I would say that yes, the 1990's were almost two decades ago, and so is the entirely artificial construction of having to "suspend". In fact, almost all of the devices sold these days (and a huge amount of all 2015 laptops) do not even have the ability to enter S3 state or anything that would remotely resemble that.

Thus, many current users of suspend are actually using it in order to "freeze user space, make some drivers do a bunch of other unrelated stuff" aspect of it. And it is because you're (ab)using suspend like this that you find yourself making a fuss because of a few seconds delay during suspend.

If you want to freeze user space, use the proper kernel functionality for that. If cgroups is too complicated, fix it. If your drivers do weird stuff during suspend, fix the drivers so that they also work with dynpm.

Suspend these days is 99% policy, 1% hw/firmware stuff. Therefore: move as many decisions as possible to userspace. At some point, it will be clear the entire concept is just a relic required to support a glitchy hardware feature that happened to be very useful during the 90s and 00s.

Trading off safety and performance in the kernel

Posted May 24, 2015 6:50 UTC (Sun) by simoncion (guest, #41674) [Link] (5 responses)

> In fact, almost all of the devices sold these days (and a huge amount of all 2015 laptops) do not even have the ability to enter S3 state or anything that would remotely resemble that.

Citation *seriously* needed. S3 is Suspend To Ram. Page 12 of this 2014 Intel datasheet [0] indicates that a large number of mobile i3, i5, and i7 processors support S0, S3, S4, and S5 mode. (Check page 10 for the list of processors.)

[0] http://www.intel.com/content/dam/www/public/us/en/documen...

Trading off safety and performance in the kernel

Posted May 30, 2015 14:43 UTC (Sat) by javispedro (guest, #83660) [Link] (4 responses)

This very website: http://lwn.net/Articles/580451/

Trading off safety and performance in the kernel

Posted May 30, 2015 16:08 UTC (Sat) by cesarb (subscriber, #6266) [Link] (3 responses)

> This very website: http://lwn.net/Articles/580451/

From that link: "They expect this mode to be used, as can be seen by the fact that machines that do not support the ACPI "S3" sleep state (a.k.a. suspend) at all will start shipping soon."

IMHO "machines [...] will start shipping soon" != "almost all of the devices sold these days (and a huge amount of all 2015 laptops)". So yeah, citation still needed.

Trading off safety and performance in the kernel

Posted May 30, 2015 16:34 UTC (Sat) by javispedro (guest, #83660) [Link] (2 responses)

Let's integrate by parts: "almost all of the devices sold these days" do not support S3, since currently the only non-negliglible architecture where S3 is supported is x86, and x86 is clearly a minority of "all devices sold these days", which includes ARM smartphones and tables, µC and other embedded devices.

The other part, "a huge amount of all 2015 laptops" do not support S3, is what should be apparent from the link I sent. The Microsoft logo requirements for Windows 8 laptops/tablets/hybrids recommend Connected Standby support. When Connected Standby support is present, the firmware _must disable_ S3 support; this is a Microsoft logo _requirement_ ( e.g. http://www.anandtech.com/show/8038/windows-81-x64-connect... ) and therefore every system out there which supports Connected Standby and Windows 8 _does not support S3_.

In 2014 the first systems with that started to ship (hybrids -- including the Surface Pro, the Dell Venue Pros, last Sony Vaios, the new Helix, etc.). _All_ hybrids and tablets from 2014 already shipped with Connected Standby, but only a few laptops. If you know of any hybrid/tablet that shipped in late 2014 without CS/AOAC please let me know.

Now it's 2015, and, even within laptops, it's hard to find a system not shipping with connected standby. The Dell XPS, the new Yoga and LaVie ThinkPads, the Asus Zenbooks all ship with Connected Standby.

However, it is a fact that there are some laptops left without Connected Standby, which (supposedly) still support S3. Which is why I said "a huge amount of all 2015 laptops", and not "all of 2015 laptops". Two examples: the Thinkpad X250 and the HP Spectre x360 do not support CS, to be best of my knowledge.

Hope this explains it.

Trading off safety and performance in the kernel

Posted Sep 11, 2015 6:18 UTC (Fri) by mcortese (guest, #52099) [Link] (1 responses)

Now it's 2015, and, even within laptops, it's hard to find a system not shipping with connected standby

Funny. I see that most laptops still come with spinning disk: they shouldn't support Connected Standby as SSD is listed as a requirement. What am I missing?

Trading off safety and performance in the kernel

Posted Oct 20, 2015 22:35 UTC (Tue) by javispedro (guest, #83660) [Link]

> I see that most laptops still come with spinning disk

At least in the country where I live, only 2 out of the 20 most sold laptops in Amazon contain a spinning disk. Those 2 peculiarly enough ship with Windows 7.

In fact, there are more laptops sold with eMMCs than spinning drives. I always learn something...