On Tue, 2007-10-02 at 22:06 +0200, Aurelien Jarno wrote: > Hi, Hi,
> As announced by Ralf Baechle, dyntick is now available on MIPS. I gave a > try on QEMU/MIPS, and unfortunately it doesn't work correctly. > > In some cases the kernel schedules an event very near in the future, > which means the timer is scheduled a few cycles only from its current > value. Unfortunately under QEMU, the timer runs too fast compared to the > speed at which instructions are execution. This causes a lockup of the > kernel. This can be triggered by running hwclock --hctosys in the guest > (which is run at boot time by most distributions). Until now, I haven't > found any other way to trigger the bug. [....] There seem to have specific problems when using dynticks in Qemu. What I can see is that it makes the PowerPC emulation quite unusable, at least on my PC, which is an amd64 (with a fix CPU frequency), no matter if I run 32 or 64 bits mode. What I can see is that the emulated timer frequency seem to be completely random: the system time, as seen from the target CPU, is running from half of the real time to twice of the real time speed, randomly; launching Qemu twice in the same conditions, on the same machine, will give different speed for the emulated system timer. I also experiment a lot of Qemu freezes: I cannot run the emulated target more than a few minutes before it freezes; sometimes it runs less than 1 second, even not get out of the firmware. It's not the same issue than yours, as the firmware uses no timer and as it's a complete Qemu freeze: even the monitor is frozen. I tried to disactivate dynticks, just commenting the entry in alarm_timers structure. Since then, I can notice that the emulated system clock seems always to be running at the same speed as the host one (not a single second of difference after 2 hours of compilation in the target system...) and that I never had any Qemu freeze anymore since then. Which convinces me that dynticks is the source of the problems... Then, I feel like dynticks in Qemu is an experimental feature that should not be activated as default, as it seems not to be really usable as it is now. I got no idea of what's going wrong in that code, I saw nothing awfull at first sight (I only gave a quick look...) but it makes Qemu unreliable and quite unusable, as far as I can see. [...] -- J. Mayer <[EMAIL PROTECTED]> Never organized
