On Mon, Aug 05, 2024 at 11:38:23AM -0700, Evan Green wrote: > On Mon, Aug 5, 2024 at 10:38 AM Jesse Taube <jesse@xxxxxxxxxxxx> wrote: > > > > Add a kernel parameter to the unaligned access speed. This allows > > skiping of the speed tests for unaligned accesses, which often is very > > slow. > > > > Signed-off-by: Jesse Taube <jesse@xxxxxxxxxxxx> > > How come this is a command line parameter rather than a Kconfig > option? I could be wrong, so I'll lay out my rationale and people can > pick it apart if I've got a bad assumption. > > I think of commandline parameters as (mostly) something end users > twiddle with, versus kconfig options as something system builders set > up. I'd largely expect end users not to notice two ticks at boot time. > I'd expect its system builders and fleet managers, who know their > hardware and build their kernels optimized for it, are the ones who > would want to shave off this time and go straight to the known answer. > Anecdotally, at ChromeOS we had a strong preference for Kconfig > options, as they were easier to compose and maintain than a loose pile > of commandline arguments. > > The commit text doesn't go into the rationale, intended audience, or > expected usage, so maybe my guesses miss the mark on what you're > thinking. > -Evan There was a brief discussion about this on Jesse's series about vector unaligned support [1]. The original idea was to use Zicclsm to allow people to set the unaligned access speed on pre-compiled distro kernels. However Zicclsm isn't useful so the alternative route was to use a kernel arg. There is already support for a Kconfig, the kernel arg is just another option for users. Link: https://lore.kernel.org/lkml/af3152b6-adf7-40fa-b2a1-87e66eec45b0@xxxxxxxxxxxx/ [1] - Charlie
