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    SubjectRe: [PATCH v9 0/5] Add NUMA-awareness to qspinlock
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    > On Jan 26, 2020, at 5:42 PM, Paul E. McKenney <paulmck@kernel.org> 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
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