On 08/28/2017 11:41 AM, Jan Beulich wrote: >>>> On 28.08.17 at 16:35, <boris.ostrov...@oracle.com> wrote: >> On 08/28/2017 03:38 AM, Jan Beulich wrote: >>>>> And finally I continue to be not really happy about the change as >>>>> a whole. Despite what was discussed on v1, I'm concerned of the >>>>> effects of this on hosts _not_ suffering from vector shortage. >>>>> Could you live with the new behavior requiring a command line >>>>> option to enable? >>>> I can add something like 'apic_share_vectors', defaulting to true, >>>> although it will not be useful in case of a hotplug. Defaulting to false? >>> Along the lines of the above plus our desire to limit the number >>> of top level options, how about "apic=isolate-vectors"? >>> >>> Also I don't understand your reference to hotplug, nor why you >>> suggest two opposite default values. >> Not two, just one --- not share vectors by default. >> >> As for hotplug, I was thinking of a case where a system is successfully >> booted with shared vectors but then a device is added and we fail to >> find enough free vectors. So the administrator would need to know in >> advance whether a new card might be coming in. >> >> When defaulting to false (as in apic_share_vectors=false) if the >> administrator decides to set it to true then he would be in some sense >> explicitly agreeing to never plug anything in (or at least to tolerate >> such a failure). > Ah, I see. But imo the default ought to be current behavior. > >>> But finally, you agreeing to a command line option here makes >>> me come back to an earlier suggestion: Didn't we agree that >>> "x2apic_phys" would be sufficient to eliminate the issue? In which >>> case no patch would be needed at all. >> x2apic_phys means that we never share vectors. With 'isolate-vectors' >> option we are still able to share them if the mask is explicitly specified. > Well, aiui your primary goal is to address the vector shortage. For > that you don't need the new option, you can get away with the > existing one.
I don't have any numbers to prove (or disprove) that not sharing vectors during boot but possibly sharing them later improves performance so yes, x2apic_phys is a possible solution. Especially if with this (modified) patch we'd default to original cluster mode behavior as you are suggesting. -boris _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel