Messages in this thread |  | | Date | Tue, 05 Nov 2013 13:54:30 -0800 | From | David Cohen <> | Subject | Re: [PATCH v4 2/4] usb: gadget: add quirk_ep_out_aligned_size field to struct usb_gadget |
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On 11/05/2013 10:13 AM, David Cohen wrote: > 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.
At a second though, it's even better to drop both 'if' cases. I can just return round_up(...) directly.
Br, David
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