[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC] x86/smpboot: Set safer __max_logical_packages limit
Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > On Thu, Apr 20, 2017 at 03:24:53PM +0200, Vitaly Kuznetsov wrote: >> In this patch I suggest we set __max_logical_packages based on the >> max_physical_pkg_id and total_cpus, > > So my 4 socket 144 CPU system will then get max_physical_pkg_id=144, > instead of 4. > > This wastes quite a bit of memory for the per-node arrays. Luckily most > are just pointer arrays, but still, wasting 140*8 bytes for each of > them. > >> this should be safe and cover all >> possible cases. Alternatively, we may think about eliminating the concept >> of __max_logical_packages completely and relying on max_physical_pkg_id/ >> total_cpus where we currently use topology_max_packages(). >> >> The issue could've been solved in Xen too I guess. CPUID returning >> x86_max_cores can be tweaked to be the lowerest(?) possible number of >> all logical packages of the guest. > > This is getting ludicrous. Xen is plain broken, and instead of fixing > it, you propose to somehow deal with its obviously crack induced > behaviour :-( Totally agree and I don't like the solution I propose (and that's why this is RFC)... The problem is that there are such Xen setups in the wild and with the recent changes some guests will BUG() :-( Alternatively, we can just remove the BUG() and do something with CPUs which have their pkg >= __max_logical_packages, e.g. assign them to the last package. Far from ideal but will help to avoid the regression. -- Vitaly _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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