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Subject: Re: [PATCH RESEND v2 1/4] cpuidle-haltpoll: ensure grow start value
 is nonzero
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Joao Martins <joao.m.martins@oracle.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        kvm-devel <kvm@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>
References: <1573041302-4904-1-git-send-email-zhenzhong.duan@oracle.com>
 <1573041302-4904-2-git-send-email-zhenzhong.duan@oracle.com>
 <CAJZ5v0gyszPOvUxd8WX8gxc1OvX_nLUGh3vKn=aXWRj52L76yw@mail.gmail.com>
From:   Zhenzhong Duan <zhenzhong.duan@oracle.com>
Organization: Oracle Corporation
Message-ID: <4219f339-556d-e2f8-c54a-99c6bc83eafd@oracle.com>
Date:   Sun, 17 Nov 2019 17:02:31 +0800
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On 2019/11/15 18:26, Rafael J. Wysocki wrote:
> On Wed, Nov 6, 2019 at 12:56 PM Zhenzhong Duan
> <zhenzhong.duan@oracle.com> 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@oracle.com>
>> ---
>>   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
>>