On Wed, 21 Nov 2018 09:30:34 +0100 Michael Mueller <mimu@xxxxxxxxxxxxx> wrote: > On 20.11.18 12:33, Cornelia Huck wrote: > > On Mon, 19 Nov 2018 18:25:25 +0100 > > Michael Mueller <mimu@xxxxxxxxxxxxx> wrote: > > > >> Do not call __deliver_io() for adapter interruptions already > >> pending in the IPM. That is a double effort. They will > >> be processed as soon the vcpu control is given to SIE. > >> > >> Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx> > >> --- > >> arch/s390/kvm/interrupt.c | 54 ++++++++++++++++++++++------------------------- > >> 1 file changed, 25 insertions(+), 29 deletions(-) > > > > I think this patch does what it says on the tin, but I'm a bit lost as > > to the why. (Might make more sense with the gib.) > > > > Currently, we are trying to process any I/O interrupts, even if we'd > > get them delivered via the gisa, when we're out of the SIE anyway. > > IIRC, while this looks a bit like a belt-and-suspenders approach, it > > also prevented performance problems when the vcpu did not go back into > > the SIE immediately (it even may exit to userspace). > > > > Also, if you're ignoring the I/O interrupts pending in the ipm, you may > > end up delivering interrupts with a lower priority (higher isc) first. > > I'm not sure that's what we want. > > > > But maybe I'm just missing another bit of the code that makes this > > safe. Can you elaborate a bit? > > > Function kvm_s390_deliver_pending_interrupts() is called in the > beginning of vcpu_pre_run() and we are about to enter the SIE anyway. > SIE will also grant the right ISC priority for adapter interruptions. > > I basically want to avoid that a GISA that is part of the alert list > will get its IPM bits cleared outside the GIB alert interruption > context. process_gib_alert_list() Unfinished sentence? Anyway, I think the patch description would benefit from adding a sentence or two describing possible performance benefits and ease of alert handling when the gib is introduced (?)
