On Mon, Jan 27, 2020 at 09:11:43AM -0500, Waiman Long wrote: > On 1/26/20 5:42 PM, 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? > Do you mean within the VM, lscpu showed that the system has one node and > 12 threads per node? If that is the case, it should behave like regular > qspinlock and be fair. I mean that I saw this in dmesg, which I believe to be telling me the same thing as lscpu saying that there is one node, but you tell me! [ 0.007106] No NUMA configuration found [ 0.007107] Faking a node at [mem 0x0000000000000000-0x000000001ffdefff] [ 0.007111] NODE_DATA(0) allocated [mem 0x1ffdb000-0x1ffdefff] [ 0.007126] Zone ranges: [ 0.007127] DMA [mem 0x0000000000001000-0x0000000000ffffff] [ 0.007128] DMA32 [mem 0x0000000001000000-0x000000001ffdefff] [ 0.007128] Normal empty [ 0.007129] Movable zone start for each node [ 0.007129] Early memory node ranges [ 0.007130] node 0: [mem 0x0000000000001000-0x000000000009efff] [ 0.007132] node 0: [mem 0x0000000000100000-0x000000001ffdefff] [ 0.007227] Zeroed struct page in unavailable ranges: 98 pages [ 0.007227] Initmem setup node 0 [mem 0x0000000000001000-0x000000001ffdefff] [ 0.007228] On node 0 totalpages: 130941 [ 0.007231] DMA zone: 64 pages used for memmap [ 0.007231] DMA zone: 21 pages reserved [ 0.007232] DMA zone: 3998 pages, LIFO batch:0 [ 0.007266] DMA32 zone: 1984 pages used for memmap [ 0.007267] DMA32 zone: 126943 pages, LIFO batch:31 > > 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? > > You can certainly play around with CNA in a VM. However, it is generally > not recommended to use CNA in a VM unless the VM cpu topology matches > the host with 1-to-1 vcpu pinning and there is no vcpu overcommit. In > this case, one may see some performance improvement using CNA by using > the "numa_spinlock=on" option to explicitly turn it on. Sorry, but I will not be booting this on bare metal on the systems that I currently have access to. No more than I run rcutorture on bare metal on them, especially not with newly modified variants of RCU. ;-) > Because of the shuffling of queue entries, CNA is inherently less fair > than the regular qspinlock. However, a ratio of 5 seems excessive to me. > vcpu preemption may be a factor in contributing to this large variation. > My testing on bare metal only showed a throughput variation within > 10-20% at most. OK. Any guidance on qemu's -numa, or should I just experiment with it? The latter will take me some time, as I must focus on other things this week. Alternatively, would it make sense for you to give it a spin in a VM? After all, it is entirely possible that I still have some configuration or another messed up. Thanx, Paul
