On 11/05/2013 07:41 AM, Alan Stern wrote:
> On Tue, 5 Nov 2013, David Cohen wrote:
>
>>>> +static inline size_t usb_ep_align_maxpacketsize(struct usb_ep *ep, size_t len)
>>>> +{
>>>> + int aligned;
>>>> +
>>>> + if (ep->desc->bmAttributes & USB_ENDPOINT_XFER_INT)
>>>> + /*
>>>> + * Interrupt eps don't need max packet size to be power of 2,
>>>> + * so can't use cheap IS_ALIGNED() macro.
>>>> + */
>>>> + aligned = !(len % ep->desc->wMaxPacketSize);
>>>> + else
>>>> + aligned = IS_ALIGNED(len, ep->desc->wMaxPacketSize);
>>>
>>> This isn't on a hot path, and I suspect that the extra "if" will
>>> require nearly as much time as you save by not doing the division. You
>>> might as well always use the % operation.
>>
>> Perhaps if I use unlikely() on 'if' condition instead?
>> Anyway I'll double check the costs of if + IS_ALIGNED vs modulo.
>
> You're missing the point. You and I (not to mention anybody who ever
> reads this code in the future) have already wasted more time talking
> about it and trying to understand it than you will ever save by using
> IS_ALIGNED.
>
> The difference to the computer is minimal at best. Make things easier
> for the programmers.
I don't see it as complex :)
But I'm fine with your proposal. I can send new patch dropping
IS_ALIGNED() case.
Br, David Cohen
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