On Sun, Jan 26, 2020 at 02:42:45PM -0800, Paul E. McKenney 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! > > 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 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? And the reader-writer lock run also shows "Enabling CNA spinlock". Same hardware and same 30-minute duration. Writes: Total: 25556912 Max/Min: 3225161/1664621 Fail: 0 Reads : Total: 11530762 Max/Min: 1155679/794179 Fail: 0 These are both within a factor of two (1.9 and 1.5), hence no "???". Thanx, Paul
