> On Jan 26, 2020, at 5:42 PM, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > On Sun, Jan 26, 2020 at 07:35:35AM -0800, Paul E. McKenney wrote: >> On Sat, Jan 25, 2020 at 02:41:39PM -0500, Waiman Long wrote: >>> On 1/24/20 11:58 PM, Paul E. McKenney wrote: >>>> On Fri, Jan 24, 2020 at 09:17:05PM -0500, Waiman Long wrote: >>>>> On 1/24/20 8:59 PM, Waiman Long wrote: >>>>>>> You called it! I will play with QEMU's -numa argument to see if I can get >>>>>>> CNA to run for me. Please accept my apologies for the false alarm. >>>>>>> >>>>>>> Thanx, Paul >>>>>>> >>>>>> CNA is not currently supported in a VM guest simply because the numa >>>>>> information is not reliable. You will have to run it on baremetal to >>>>>> test it. Sorry for that. >>>>> Correction. There is a command line option to force CNA lock to be used >>>>> in a VM. Use the "numa_spinlock=on" boot command line parameter. >>>> As I understand it, I need to use a series of -numa arguments to qemu >>>> combined with the numa_spinlock=on (or =1) on the kernel command line. >>>> If the kernel thinks that there is only one NUMA node, it appears to >>>> avoid doing CNA. >>>> >>>> Correct? >>>> >>>> Thanx, Paul >>>> >>> In auto-detection mode (the default), CNA will only be turned on when >>> paravirt qspinlock is not enabled first and there are at least 2 numa >>> nodes. The "numa_spinlock=on" option will force it on even when both of >>> the above conditions are false. >> >> Hmmm... >> >> Here is my kernel command line taken from the console log: >> >> console=ttyS0 locktorture.onoff_interval=0 numa_spinlock=on locktorture.stat_interval=15 locktorture.shutdown_secs=1800 locktorture.verbose=1 >> >> Yet the string "Enabling CNA spinlock" does not appear. >> >> Ah, idiot here needs to enable CONFIG_NUMA_AWARE_SPINLOCKS in his build. >> Trying again with "--kconfig "CONFIG_NUMA_AWARE_SPINLOCKS=y"... > > And after fixing that, plus adding the other three Kconfig options required > to enable this, I really do see "Enabling CNA spinlock" in the console log. > Yay! Great! Your persistence paid off :) Yet, CNA does not do much interesting here, as it sees only one numa node. > > At the end of the 30-minute locktorture exclusive-lock run, I see this: > > Writes: Total: 572176565 Max/Min: 54167704/10878216 ??? Fail: 0 > > This is about a five-to-one ratio. Is this expected behavior, given a > single NUMA node on a single-socket system with 12 hardware threads? I’m not sure what is expected here. I’m guessing that if you boot your guest with the default (non-CNA/non-paravirt) qspinlock, you will get a similar result. > > I will try reader-writer lock next. > > Again, should I be using qemu's -numa command-line option to create nodes? > If so, what would be a sane configuration given 12 CPUs and 512MB of > memory for the VM? If not, what is a good way to exercise CNA's NUMA > capabilities within a guest OS? That’s a good question. Perhaps Longman knows the answer? Regards, — Alex
