On Wed, Aug 16, 2017 at 5:45 PM, Dario Faggioli <dario.faggi...@citrix.com> wrote: > In fact, right now, we read it at every iteration of the loop. > The reason it's done like this is how context switch was handled > on IA64 (see commit ae9bfcdc, "[XEN] Various softirq cleanups" [1]). > > However: > 1) we don't have IA64 any longer, and all the achitectures that > we do support, are ok with sampling once and for all; > 2) sampling at every iteration (slightly) affect performance; > 3) sampling at every iteration is misleading, as it makes people > believe that it is currently possible that SCHEDULE_SOFTIRQ > moves the execution flow on another CPU (and the comment, > by reinforcing this belief, makes things even worse!). > > Therefore, let's: > - do the sampling only once, and remove the comment; > - leave an ASSERT() around, so that, if context switching > logic changes (in current or new arches), we will notice. > > [1] Some more (historical) information here: > > http://old-list-archives.xenproject.org/archives/html/xen-devel/2006-06/msg01262.html > > Signed-off-by: Dario Faggioli <dario.faggi...@citrix.com> > Reviewed-by: George Dunlap <george.dun...@eu.citrix.com> > --- > Cc: Andrew Cooper <andrew.coop...@citrix.com> > Cc: Jan Beulich <jbeul...@suse.com> > Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> > Cc: Stefano Stabellini <sstabell...@kernel.org> > Cc: Julien Grall <julien.gr...@arm.com> > Cc: Tim Deegan <t...@xen.org> > --- > This has been submitted already, as a part of another series. Discussion is > here: > https://lists.xen.org/archives/html/xen-devel/2017-06/msg00102.html > > For the super lazy, Jan's latest word in that thread were these: > "I've voiced my opinion, but I don't mean to block the patch. After > all there's no active issue the change introduces." > (https://lists.xen.org/archives/html/xen-devel/2017-06/msg00797.html) > > Since then: > - changed "once and for all" with "only once", as requested by George (and > applied his Reviewed-by, as he said I could).
The commit message, but forgot to change the title. :-) That can be addressed on check-in if need be. -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
