Re: [Qemu-devel] [Qemu-arm] [PATCH v2 0/5] hw: arm: exynos: Bring up secondary CPU + CPUIDLE issue

[Alex Bennée]

That means you're on a pre-mttcg tree so that's not the reason.

On 14 Mar 2017 5:35 pm, "Krzysztof Kozlowski" <address@hidden> wrote:

> On Tue, Mar 14, 2017 at 04:55:34PM +0000, Alex Bennée wrote:
> >
> > Krzysztof Kozlowski <address@hidden> writes:
> >
> > > Hi,
> > >
> > <snip>
> > >
> > > Overview of the problem
> > > =======================
> > > On Exynos4210, by default Linux kernel uses cpuidle driver which tries
> > > to enter low power mode, called AFTR (Arm Off, Top Running).  On real
> > > hardware this brings some power savings.  This AFTR mode requires
> second
> > > CPU to be off, so the driver (coupled cpuidle driver) when system is
> idle:
> > > 1. Turns off second CPU,
> > > 2. Enters AFTR on CPU0.
> > >
> > > However the QEMU system is then totally unresponsive (e.g. on serial
> console)
> > > and RCU stalls appear from time to time.  I spent some time on it and
> did not
> > > find the real cause behind the lag.  Maybe it is because the second CPU
> > > does not really power down itself and system just burns the cycles
> under spin
> > > locks?
> >
> > Was this tested post the MTTCG merge? Maybe there is an interaction
> > between power saving/halting the vCPU?
> >
> > I mention this because I already made some minor tweaks for handing the
> > WFI instruction in MTTCG. See commit c22edfebff. You can test this by
> > forcing the original behaviour by adding:
> >
> >   -accel tcg,thread=single
> >
> > to your command line.
> >
>
> I am testing it on v2.8.0-2005-g17783ac828ad. Without any -accel, the
> system boots but responsiveness of serial console is bad. Bad but at
> least it is responding still a little bit.
>
> With the -accel you mentioned, system does not even reach user-space
> (initramfs).
>
> I tried rebasing on newer (e.g. v2.8.0-2182-g5e2fb7c598c6) but
> compilation fails all the time on:
> /home/dev/qemu/qemu/vl.c: In function ‘main’:
> /home/dev/qemu/qemu/vl.c:3131:18: error: ‘QEMU_OPTION_blockdev’
> undeclared (first use in this function)
>              case QEMU_OPTION_blockdev:
>
>
> Best regards,
> Krzysztof
>
>