On Thu, Sep 24, 2020 at 08:21:07PM +0200, Thomas Gleixner wrote: > On Thu, Sep 24 2020 at 08:33, Greg KH wrote: > > On Wed, Sep 23, 2020 at 05:08:32PM -0700, Prasad Sodagudi wrote: > >> +config CONSOLE_FLUSH_ON_HOTPLUG > >> + bool "Enable console flush configurable in hot plug code path" > >> + depends on HOTPLUG_CPU > >> + def_bool n > > > > n is the default, no need to list it. > > > >> + help > >> + In cpu hot plug path console lock acquire and release causes the > >> + console to flush. If console lock is not free hot plug latency > >> + increases. So make console flush configurable in hot plug path > >> + and default disabled to help in cpu hot plug latencies. > > > > Why would you not want this option? > > > > Why isn't this just a bugfix? > > Because it's the normal behaviour of console lock and there are > gazillion other ways to delay stuff in the hotplug path. > > CPU hotplug is not meant to be a high speed operation and if people > think they need it to be fast then its pretty much guaranteed that they > want it for the completely wrong reasons.
Odds are, it's the big/little systems that are trying to use cpu hotplug for this type of thing :( > This #ifdef tinkering is just digusting especially as it just tackles an > obvious way how to delay timer migration, but does not address the > underlying root cause. Agreed, thanks for putting it better than I did. greg k-h
