Re: [Qemu-devel] [PATCH] qemu-timer: remove unnecessary code

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/07/2016 13:40, Cao jin wrote:
> 
> 
> On 07/13/2016 06:21 PM, Paolo Bonzini wrote:
>>
>>
>> On 13/07/2016 11:06, Cao jin wrote:
>>> When passed argument 'ns' is 0, macro DIV_ROUND_UP will return 0 also.
>>
>> It's potentially slower though.
>>
> 
> Is it because the function in the i/o loop path, so the potentially
> extra arithmetical instructions matters?

It is quite common for ns to be zero, for example if a bottom half has
to be invoked.

However, qemu_timeout_ns_to_ms is not used in the really important path
(which is aio_poll in aio-posix.c) so I guess your patch is okay.

Thanks,

Paolo

>> Paolo
>>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
>>> ---
>>>   qemu-timer.c | 6 +-----
>>>   1 file changed, 1 insertion(+), 5 deletions(-)
>>>
>>> diff --git a/qemu-timer.c b/qemu-timer.c
>>> index eb22e92..cfe0893 100644
>>> --- a/qemu-timer.c
>>> +++ b/qemu-timer.c
>>> @@ -285,12 +285,8 @@ int qemu_timeout_ns_to_ms(int64_t ns)
>>>           return -1;
>>>       }
>>>
>>> -    if (!ns) {
>>> -        return 0;
>>> -    }
>>> -
>>>       /* Always round up, because it's better to wait too long than
>>> to wait too
>>> -     * little and effectively busy-wait
>>> +     * short and effectively busy-wait
>>>        */
>>>       ms = DIV_ROUND_UP(ns, SCALE_MS);
>>>
>>>
>>
>>
>>
>