Re: [PATCH 0/4] Introduce QPW for per-cpu operations

[Michal Hocko]

On Fri 20-02-26 16:01:59, Marcelo Tosatti wrote:
> On Fri, Feb 20, 2026 at 06:58:10PM +0100, Vlastimil Babka wrote:
[...]
> > >> So if we can assume that workloads on isolated cpus make syscalls only
> > >> rarely, and when they do they can tolerate them being slower, I think the
> > >> "avoid sheaves on isolated cpus" would be the best way here.
> > > 
> > > I am not sure its safe to assume that. Ask Gemini about isolcpus use
> > > cases and:
> > 
> > I don't think it's answering the question about syscalls. But didn't read
> > too closely given the nature of it.
> 
> People use isolcpus with all kinds of programs. 
> 
> > > For example, AF_XDP bypass uses system calls (and wants isolcpus):
> > > 
> > > https://www.quantvps.com/blog/kernel-bypass-in-hft?srsltid=AfmBOoryeSxuuZjzTJIC9O-Ag8x4gSwjs-V4Xukm2wQpGmwDJ6t4szuE
> > 
> > Didn't spot system calls mentioned TBH.
> 
> I don't see why you want to reduce performance of applications that 
> execute on isolcpus=, if you can avoid that.

If you can avoid that by making performance bad for everybody else then
then it seems safer to sacrifice those workloads that are much more
special - i.e. cpu isolation.
-- 
Michal Hocko
SUSE Labs