On Wed, 2017-05-03 at 12:17 -0400, Doug Ledford wrote: > On 5/3/2017 11:58 AM, Bart Van Assche wrote: > > On Wed, 2017-05-03 at 09:53 -0600, Jason Gunthorpe wrote: > > > On Wed, May 03, 2017 at 05:19:27PM +0200, Marta Rybczynska wrote: > > > > > > > > where > > > > > queue->sig_limit = max(queue->queue_size / 2, 1); > > > > > > > > I tried to avoid that because this adds a division in the fast path Bart > > > > was unhappy about in v2. > > > > > > The compiler switches divide/multiply by powers of two into fast bit shifts. > > > > Hello Jason, > > > > As far as I know the compiler only does that for compile-time constants. In > > this case the divisor (max(queue_size / 2, 1)) is not a compile-time constant. > > Sure it is. The only thing that needs to be constant for the compiler > to do the right thing is the '/ 2' part. queue_size need not be > constant, and the max is performed after the division. I would fully > expect the compiler to get this right and convert it internally to the > equivalent bit shift, but if it didn't you could always just write it > that way in the first place: > > queue->sig_limit = max(queue->queue_size >> 1, 1); Hello Doug, In my comment I was referring to "% max(queue_size / 2, 1)" and not to "queue_size / 2". Bart.-- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
