On 10/02/2021 18.57, Paul E. McKenney wrote: > On Wed, Feb 10, 2021 at 06:26:54PM +0200, Andy Shevchenko wrote: >> On Tue, Feb 09, 2021 at 05:58:59PM -0500, Paul Gortmaker wrote: >>> The basic objective here was to add support for "nohz_full=8-N" and/or >>> "rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference >>> to the last core, evaluated at boot for anything using a CPU list. >> >> I thought we kinda agreed that N is confusing and L is better. >> N to me is equal to 32 on 32 core system as *number of cores / CPUs*. While L >> sounds better as *last available CPU number*. > > The advantage of "N" is that people will automatically recognize it as > "last thing" or number of things" because "N" has long been used in > both senses. In contrast, someone seeing "0-L" for the first time is > likely to go "What???".
Completely agree. The patch that introduces this even updates Documentation/ at the same time, and if people are confused just because they don't RTFM, xkcd#293 applies. So let's please just paint the bikeshed N. (As for case insensitivity, I don't see the point, it just makes documentation and implementation more cumbersome and confusing. Just document and implement _one_ way of doing this.) As for a future syntax for "last 4 cpus", it's common to accept a negative index to mean count from the end, so unless we already accept -4 as a shorthand for 0-4 (haven't checked), that could be -4-N. But regardless, I also agree with Paul on this point, that's for a future time when the need arises. Rasmus