On Fri, 2019-05-17 at 15:10 +0200, Thomas Huth wrote:
> On 17/05/2019 15.03, Laurent Vivier wrote:
> > From: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> >
> > Currently the handler for a decrementer exception will simply
> > reload the
> > maximum value (0x7FFFFFFF), which will take ~4 seconds to expire
> > again.
> > This means that if a vcpu cedes, it will be ~4 seconds between
> > wakeups.
> >
> > The h_cede_tm test is testing a known breakage when a guest cedes
> > while
> > suspended. To be sure we cede 500 times to check for the bug.
> > However
> > since it takes ~4 seconds to be woken up once we've ceded, we only
> > get
> > through ~20 iterations before we reach the 90 seconds timeout and
> > the
> > test appears to fail.
> >
> > Add an option when registering the decrementer handler to specify
> > the
> > value which should be reloaded by the handler, allowing the timeout
> > to be
> > chosen.
> >
> > Modify the spr test to use the max timeout to preserve existing
> > behaviour.
> > Modify the h_cede_tm test to use a 10ms timeout to ensure we can
> > perform
> > 500 iterations before hitting the 90 second time limit for a test.
> >
> > This means the h_cede_tm test now succeeds rather than timing out.
> >
> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> > Reviewed-by: Thomas Huth <thuth@xxxxxxxxxx>
> > Reviewed-by: Laurent Vivier <lvivier@xxxxxxxxxx>
> > [lv: reset initial value to 0x3FFFFFFF]
>
> Looks like something went wrong here? There is still the 0x7FFFFFFF
> in
> the hunk below...
No, I think this is correct.
Max value is ox7FFFFFFF, but the initial value we load via mtdec is the
original 0x3FFFFFFF.
>
> > diff --git a/powerpc/sprs.c b/powerpc/sprs.c
> > index 6744bd8d8049..3c2d98c9ca99 100644
> > --- a/powerpc/sprs.c
> > +++ b/powerpc/sprs.c
> > @@ -253,6 +253,7 @@ int main(int argc, char **argv)
> > 0x1234567890ABCDEFULL, 0xFEDCBA0987654321ULL,
> > -1ULL,
> > };
> > + static uint64_t decr = 0x7FFFFFFF; /* Max value */
> >
> > for (i = 1; i < argc; i++) {
> > if (!strcmp(argv[i], "-w")) {
> > @@ -288,7 +289,7 @@ int main(int argc, char **argv)
> > (void) getchar();
> > } else {
> > puts("Sleeping...\n");
> > - handle_exception(0x900, &dec_except_handler,
> > NULL);
> > + handle_exception(0x900, &dec_except_handler,
> > &decr);
> > asm volatile ("mtdec %0" : : "r" (0x3FFFFFFF));
> > hcall(H_CEDE);
> > }
>
> Thomas
