From: Geert Uytterhoeven > Sent: 11 June 2021 07:55 > Hi Dave, > > On Fri, Jun 11, 2021 at 12:02 AM Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Thu, Jun 10, 2021 at 01:00:01PM +0200, Geert Uytterhoeven wrote: ... > > 64 bit division on 32 bit platforms is still a problem in this day > > and age? > > They're not a problem. But you should use the right operations from > <linux/math64.h>, iff you really need these expensive operations. (64bit) division isn't exactly cheap on 64bit cpus. Some timing tables for x86 give latencies of well over 1 bit/clock for Intel cpus, AMD ryzen manage 2 bits/clock. Signed divide is also significantly more expensive than unsigned divide. Integer divide performance is clearly not important enough to throw silicon at. The same tables show fdiv having a latency of 16 clocks. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
