On 2017-11-17 19:36, Thomas Gleixner wrote:
On Fri, 17 Nov 2017, Quan Xu wrote:
On 2017-11-16 17:53, Thomas Gleixner wrote:
That's just plain wrong. We don't want to see any of this PARAVIRT crap in
anything outside the architecture/hypervisor interfacing code which really
needs it.
The problem can and must be solved at the generic level in the first place
to gather the data which can be used to make such decisions.
How that information is used might be either completely generic or requires
system specific variants. But as long as we don't have any information at
all we cannot discuss that.
Please sit down and write up which data needs to be considered to make
decisions about probabilistic polling. Then we need to compare and contrast
that with the data which is necessary to make power/idle state decisions.
I would be very surprised if this data would not overlap by at least 90%.
1. which data needs to considerd to make decisions about probabilistic polling
I really need to write up which data needs to considerd to make
decisions about probabilistic polling. At last several months,
I always focused on the data _from idle to reschedule_, then to bypass
the idle loops. unfortunately, this makes me touch scheduler/idle/nohz
code inevitably.
with tglx's suggestion, the data which is necessary to make power/idle
state decisions, is the last idle state's residency time. IIUC this data
is duration from idle to wakeup, which maybe by reschedule irq or other irq.
That's part of the picture, but not complete.
tglx, could you share more? I am very curious about it..
I also test that the reschedule irq overlap by more than 90% (trace the
need_resched status after cpuidle_idle_call), when I run ctxsw/netperf for
one minute.
as the overlap, I think I can input the last idle state's residency time
to make decisions about probabilistic polling, as @dev->last_residency does.
it is much easier to get data.
That's only true for your particular use case.
2. do a HV specific idle driver (function)
so far, power management is not exposed to guest.. idle is simple for KVM
guest,
calling "sti" / "hlt"(cpuidle_idle_call() --> default_idle_call())..
thanks Xen guys, who has implemented the paravirt framework. I can implement
it
as easy as following:
--- a/arch/x86/kernel/kvm.c
Your email client is using a very strange formatting.
my bad, I insert space to highlight these code.
This is definitely better than what you proposed so far and implementing it
as a prove of concept seems to be worthwhile.
But I doubt that this is the final solution. It's not generic and not
necessarily suitable for all use case scenarios.
yes, I am exhausted :):)
could you tell me the gap to be generic and necessarily suitable for
all use case scenarios? as lack of irq/idle predictors?
I really want to upstream it for all of public cloud users/providers..
as kvm host has a similar one, is it possible to upstream with following
conditions? :
1). add a QEMU configuration, whether enable or not, by default
disable.
2). add some "TODO" comments near the code.
3). ...
anyway, thanks for your help..
Quan
Alibaba Cloud
