Not a problem -- we change it all the time, after all. That is the only way that it can possibly keep up with a changing world, let alone improve. ;-) Thanx, Paul On Thu, Dec 20, 2018 at 08:17:35AM -0800, Mark Morrissey wrote: > Thanks, Paul.l Didn't mean to cause a book change. > > --mark > -- > Mark Morrissey, markem@xxxxxxx > Senior Instructor, Computer Science > Portland State University > > > On Wed, Dec 19, 2018 at 8:35 PM Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > wrote: > > > No, that would work. Not something I would think of because there is > > no globally accessible ceil() function in the Linux kernel. ;-) > > > > I have queued a patch with your Reported-by as shown at the end of this > > email. Please let me know if I messed anything up. > > > > Thanx, Paul > > > > On Wed, Dec 19, 2018 at 05:13:01PM -0800, Mark Morrissey wrote: > > > I agree that it is equivalent to: > > > > > > p = s * ceil(m/s) > > > > > > But why not just perform that calculation? If it is based on either > > > efficiency or clock cycles, I don't see it. I admit to not having looked > > at > > > the implementation of the ceil() library routine. If I should look at > > > ceil(), then just slap me and I will understand. > > > > > > --mark > > > -- > > > Mark Morrissey, markem@xxxxxxx > > > Senior Instructor, Computer Science > > > Portland State University > > > > > > > > > On Wed, Dec 19, 2018 at 4:45 PM Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > > wrote: > > > > > > > On Mon, Dec 17, 2018 at 01:04:37PM -0800, Mark Morrissey wrote: > > > > > Hi Paul, > > > > > > > > > > I am looking at your parallel programming book, 12/5/2018 version. In > > > > > formula E.6, you use the floor function rather than the ceiling > > function. > > > > > Is this deliberate or perhaps in error? > > > > > > > > Good question! > > > > > > > > The intent is that the "+ s - 1" in the numerator does the upwards part > > > > of the rounding, and the floor function does the rest. > > > > > > > > Or am I missing something here? It should be possible to express this > > > > in terms of the ceiling function, though that would be further removed > > > > from C code implementing this equation. > > > > > > > > Adding Alexey and the list on CC. This is on page 423 (PDF page 435) > > of > > > > > > > > > > https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.2018.12.08a.pdf > > > > ------------------------------------------------------------------------ > > > > commit 9d317176364184ad6ef55fdab5535449fb8d110d > > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > Date: Wed Dec 19 20:30:28 2018 -0800 > > > > SMPdesign: Use ceiling symbol, skip odd floor computation > > > > Equation E.6 in Quick Quiz 6.20 computes the floor function of > > "(m + 2 - 1) / s", which is just the ceiling function of "m / s". > > This commit therefore moves to this simpler formulation, on the > > strength of the ceil() function in the standard library. The fact > > that ceil() is not globally available in the Linux kernel, which > > motivated the original, seems a bit irrelevant, hence the change. > > > > Reported-by: Mark Morrissey <markem@xxxxxxx> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > > > diff --git a/SMPdesign/SMPdesign.tex b/SMPdesign/SMPdesign.tex > > index fe8f445851e3..0ba7ebd04fe6 100644 > > --- a/SMPdesign/SMPdesign.tex > > +++ b/SMPdesign/SMPdesign.tex > > @@ -1177,7 +1177,7 @@ this book. > > $m$ rounded up to the next multiple of $s$, as follows: > > > > \begin{equation} > > - p = s \left \lfloor \frac{m + s - 1}{s} \right \rfloor > > + p = s \left \lceil \frac{m}{s} \right \rceil > > \label{sec:SMPdesign:p} > > \end{equation} > > > > > >
