On 07.11.18 18:11, Henning Schild wrote:
Am Wed, 7 Nov 2018 17:17:32 +0100
schrieb Jan Kiszka <jan.kis...@siemens.com>:
On 07.11.18 16:13, Henning Schild wrote:
Am Tue, 6 Nov 2018 17:02:34 -0800
schrieb Chung-Fan Yang <sonic.tw...@gmail.com>:
Hi,
I am having some quextions about power management(PM) on x86.
As afr as I understand, there are C-states and P-states,
controlling the sleeping depth and frequency scale accrodingly, on
an x86 processor.
My question is that when I use jailhouse house to create a non-root
cell, which state it will fall into?
You will get the CPU in its full power mode, if you want any of the
other states your inmate needs to support that (PM code).
Will it be reset to C0 and full frequency? or inherit the root
state when cell is created?
Is it necessary to write some PM code in the inmates?
Only if you want to safe power, or if you need to throttle so your
BIOS does not hit you with an SMI.
Power management - better: power management moderation - is not
provided by Jailhouse so far. That means, as Henning described,
inmates are responsible to do "the right thing". That's surely not
optimal, can lead to mistakes and has to be improved (see TODO). E.g,
we just learned that calling "hlt" in the apic-demo is likely a
source of undesired latency, we should do polling or mwait with the
right level (there will be patches soonish).
Interesting. Will you switch the test to mwait or will you trap hlt and
emulate it with mwait?
No idea yet, and some tests are still pending. But it's fairly likely that we
will have to trap mwait and manage which maximum C-state the cell can request
this way. With hlt being no longer a reasonable alternative, we will likely not
be able to provide an exit-free way to wait for interrupts without burning cycles.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
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