Re: [PATCH v2 1/2] s390/appldata: Emulate virtual timer with delayed work

[Heiko Carstens <hca@linux.ibm.com>]

On Thu, Oct 08, 2026 at 07:08:27PM +0200, Gerald Schaefer wrote:
> On Tue,  6 Oct 2026 16:01:12 +0200
> Heiko Carstens <hca@linux.ibm.com> wrote:
> 
> > Emulate the virtual timer in appldata using delayed work: the work is
> > scheduled for the minimum possible wall-clock time until the
> > configured CPU-time interval elapses (remaining CPU time / number of
> > online CPUs), with a minimum delay of 100ms. The work then reads
> > per-CPU statistics of all online CPUs to check whether enough CPU time
> > has elapsed, and if so runs the registered callbacks.
> > 
> > This is slightly more expensive, but allows to subsequently remove the
> > entire vtimer infrastructure.
> > 
> > Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> > ---
> >  arch/s390/appldata/appldata_base.c | 171 ++++++++++++++++++-----------
> >  1 file changed, 107 insertions(+), 64 deletions(-)
> 
> Nice improvement, with minimum wall-clock interval 100ms. Specifying a 1ms
> CPU-time interval was possible, but did not make much sense in practice.
> On very idle systems, the resulting wall-clock interval would also have
> been around 100ms, but as soon as they do some work, it would have become
> far too frequent.
> 
> Also tested it, and on a busy system there is now no noticeable difference
> for interval values 1-100, while idle systems still behave like before.
> 
> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
> Tested-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>

Thanks a lot! Applied :)