Re: [PATCH v4 2/4] usb: gadget: add quirk_ep_out_aligned_size fieldto struct usb_gadget

[David Cohen]

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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