That means you're on a pre-mttcg tree so that's not the reason. On 14 Mar 2017 5:35 pm, "Krzysztof Kozlowski" <k...@kernel.org> wrote:
> On Tue, Mar 14, 2017 at 04:55:34PM +0000, Alex Bennée wrote: > > > > Krzysztof Kozlowski <k...@kernel.org> 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 > >
