On 12/04/2013 11:48 PM, Eduardo Habkost wrote: > On Wed, Dec 04, 2013 at 04:50:59PM +1100, Alexey Kardashevskiy wrote: >> On 12/04/2013 01:47 AM, Eduardo Habkost wrote: >>> On Tue, Dec 03, 2013 at 02:30:48PM +0100, Andreas Färber wrote: >>>> Am 03.12.2013 00:03, schrieb Alexey Kardashevskiy: >>>>> On 12/03/2013 09:09 AM, Andreas Färber wrote: >>>>>> Am 02.12.2013 18:06, schrieb Michael Tokarev: >>>>>>> 25.11.2013 07:39, Alexey Kardashevskiy wrote: >>>>>>>> Since modern POWER7/POWER8 chips can have more that 256 CPU threads >>>>>>>> (>2000 actually), remove this check from smp_parse. >>>>>>>> >>>>>>>> The CPUs number is still checked against machine->max_cpus and this >>>>>>>> check >>>>>>>> should be enough not to break other archs. >>>>>> >>>>>> "should be" is not exactly the highest level of confidence for a >>>>>> "trivial" patch... :/ >>>> [...] >>>>>> Alexey, did you actually check that, e.g., x86 machines don't break with >>>>>> 256 or 257 CPUs now? >>>>> >>>>> PC_DEFAULT_MACHINE_OPTIONS sets it to 255. And I cannot find any machine >>>>> which would not define max_cpus, have I missed any? >>>> >>>> If you've actually *checked* the other machines' code then fine with me, >>>> just say so in the commit message. :) >>> >>> I just grepped for "max_cpus" and checked every match. The largest >>> values I found were: >>> >>> hw/ppc/spapr.c: 256 >>> s390: 255 >>> pc: 255 >>> >>> All the rest had values <= 32. >>> >>> Machines with missing max_cpus value shouldn't be a problem, as >>> max_cpus==0 is interpreted as 1 by the vl.c code. >>> >>> But we still need to add a check for max_cpus > machine->max_cpus to >>> vl.c, before we eliminate the smp_parse() check. >> >> >> Since smp_parse() checks if (max_cpus >= smp_cpus), this should just work: >> >> diff --git a/vl.c b/vl.c >> index e6ed260..544165a 100644 >> --- a/vl.c >> +++ b/vl.c >> @@ -3882,9 +3882,9 @@ int main(int argc, char **argv, char **envp) >> smp_parse(qemu_opts_find(qemu_find_opts("smp-opts"), NULL)); >> >> machine->max_cpus = machine->max_cpus ?: 1; /* Default to UP */ >> - if (smp_cpus > machine->max_cpus) { >> + if (max_cpus > machine->max_cpus) { >> fprintf(stderr, "Number of SMP cpus requested (%d), exceeds max >> cpus " >> - "supported by machine `%s' (%d)\n", smp_cpus, >> machine->name, >> + "supported by machine `%s' (%d)\n", max_cpus, >> machine->name, >> machine->max_cpus); >> exit(1); >> } >> >> >>> There's also this, at main(): >>> >>> if (i == nb_numa_nodes) { >>> for (i = 0; i < max_cpus; i++) { >>> set_bit(i, node_cpumask[i % nb_numa_nodes]); >>> } >>> } >>> >>> node_cpumask[] is initialized using bitmap_new(MAX_CPUMASK_BITS), and >>> MAX_CPUMASK_BITS is 255. To fix this, we can initialize node_cpumask[] using >>> max_cpus instead, if we initialize it after smp_parse(). >> >> >> Nope. At the moment when we parse -numa in vl.c, we may not know yet what >> machine is going to be used and machines can have different max_cpus. > > This will be changed by: > > Subject: [PATCH V17 04/11] NUMA: convert -numa option to use OptsVisitor > Message-Id: <1386143939-19142-5-git-send-email-gaowanl...@cn.fujitsu.com> > http://article.gmane.org/gmane.comp.emulators.qemu/244826
Any progress with this? Thanks. >> >> For now, I would simply change MAX_CPUMASK_BITS to something crazy, like >> 16384 (2KB per numa node), I hope QEMU can survive such a memory waste :) >> >> Ok? > > I'm OK with that as long the code has proper checks in case max_cpus > gets set to a crazily large value (larger than MAX_CPUMASK_BITS) in the > far future, or if we prevent max_cpus from being larger than > MAX_CPUMASK_BITS. > -- Alexey