[Qemu-devel] Re: [patch] option -no-tsc for i386 with speedstep

[Heike C. Zimmerer]

Massimo Dal Zotto <address@hidden> writes:

> When qemu runs on an i386 cpu with speedstep enabled the clock of the
> guest os is not in sync with the clock on the host os because the
> vm_timer used for irq 0 generates interrupts at wrong rate when
> the host cpu frequency changes.
>
> The following patch fixes the problem by adding a new option -no-tsc for
> the i386 architecture which can be used to disable rdtsc when running on
> a cpu with speedstep enabled.

Unfortunately this patch, effectively replacing a single assembly
instruction by a gettimeofday() call, slows some operations down to a
degree that makes a WinXP guest on GNU/Linux host nearly unusable at
network and file system operations (at least here).

- Heike