Re: [PATCH RESEND v2 1/4] cpuidle-haltpoll: ensure grow start value is nonzero

[Zhenzhong Duan]

On 2019/11/15 18:26, Rafael J. Wysocki wrote:
> On Wed, Nov 6, 2019 at 12:56 PM Zhenzhong Duan
> <zhenzhong.duan@xxxxxxxxxx> wrote:
> > dev->poll_limit_ns could be zeroed in certain cases (e.g. by
> > guest_halt_poll_ns = 0). If guest_halt_poll_grow_start is zero,
> > dev->poll_limit_ns will never be bigger than zero.
> I would rephrase this in the following way:
>
> "If guest_halt_poll_grow_start is zero and dev->poll_limit_ns becomes
> zero for any reason, it will never be greater than zero again, so use
> ..."

OK, will do, thanks for your suggestion.

Zhenzhong

> The patch itself looks OK to me.
>
> > Use param callback to avoid writing zero to guest_halt_poll_grow_start.
> >
> > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> > ---
> >   drivers/cpuidle/governors/haltpoll.c | 22 +++++++++++++++++++++-
> >   1 file changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
> > index 7a703d2..660859d 100644
> > --- a/drivers/cpuidle/governors/haltpoll.c
> > +++ b/drivers/cpuidle/governors/haltpoll.c
> > @@ -20,6 +20,26 @@
> >   #include <linux/module.h>
> >   #include <linux/kvm_para.h>
> >
> > +static int grow_start_set(const char *val, const struct kernel_param *kp)
> > +{
> > +       int ret;
> > +       unsigned int n;
> > +
> > +       if (!val)
> > +               return -EINVAL;
> > +
> > +       ret = kstrtouint(val, 0, &n);
> > +       if (ret || !n)
> > +               return -EINVAL;
> > +
> > +       return param_set_uint(val, kp);
> > +}
> > +
> > +static const struct kernel_param_ops grow_start_ops = {
> > +       .set = grow_start_set,
> > +       .get = param_get_uint,
> > +};
> > +
> >   static unsigned int guest_halt_poll_ns __read_mostly = 200000;
> >   module_param(guest_halt_poll_ns, uint, 0644);
> >
> > @@ -33,7 +53,7 @@
> >
> >   /* value in us to start growing per-cpu halt_poll_ns */
> >   static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
> > -module_param(guest_halt_poll_grow_start, uint, 0644);
> > +module_param_cb(guest_halt_poll_grow_start, &grow_start_ops, &guest_halt_poll_grow_start, 0644);
> >
> >   /* allow shrinking guest halt poll */
> >   static bool guest_halt_poll_allow_shrink __read_mostly = true;
> > --
> > 1.8.3.1