On Wed, Apr 05, 2023 at 04:43:14PM -0300, Marcelo Tosatti wrote:

Two points:

1) For a virtualized system, the overhead is not only of executing the
IPI but:

	VM-exit
	run VM-exit code in host
	handle IPI
	run VM-entry code in host
	VM-entry

I thought we could do IPIs without VMexit these days? Also virt... /me
walks away.

2) Depends on the application and the definition of "occasional".

For certain types of applications (for example PLC software or
RAN processing), upon occurrence of an event, it is necessary to
complete a certain task in a maximum amount of time (deadline).

If the application is properly NOHZ_FULL and never does a kernel entry,
it will never get that IPI. If it is a pile of shit and does kernel
entries while it pretends to be NOHZ_FULL it gets to keep the pieces and
no amount of crying will get me to care.