On Thu, 2022-07-28 at 16:31 +1000, Nicholas Piggin wrote:
> Allow for a reduction in the number of times a CPU from a different
> node than the owner can attempt to steal the lock before queueing.
> This could bias the transfer behaviour of the lock across the
> machine and reduce NUMA crossings.
> ---
> arch/powerpc/lib/qspinlock.c | 34 +++++++++++++++++++++++++++++++---
> 1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
> index d4594c701f7d..24f68bd71e2b 100644
> --- a/arch/powerpc/lib/qspinlock.c
> +++ b/arch/powerpc/lib/qspinlock.c
> @@ -4,6 +4,7 @@
> #include <linux/export.h>
> #include <linux/percpu.h>
> #include <linux/smp.h>
> +#include <linux/topology.h>
> #include <asm/qspinlock.h>
> #include <asm/paravirt.h>
>
> @@ -24,6 +25,7 @@ struct qnodes {
>
> /* Tuning parameters */
> static int STEAL_SPINS __read_mostly = (1<<5);
> +static int REMOTE_STEAL_SPINS __read_mostly = (1<<2);
> #if _Q_SPIN_TRY_LOCK_STEAL == 1
> static const bool MAYBE_STEALERS = true;
> #else
> @@ -39,9 +41,13 @@ static bool pv_prod_head __read_mostly = false;
>
> static DEFINE_PER_CPU_ALIGNED(struct qnodes, qnodes);
>
> -static __always_inline int get_steal_spins(bool paravirt)
> +static __always_inline int get_steal_spins(bool paravirt, bool remote)
> {
> - return STEAL_SPINS;
> + if (remote) {
> + return REMOTE_STEAL_SPINS;
> + } else {
> + return STEAL_SPINS;
> + }
> }
>
> static __always_inline int get_head_spins(bool paravirt)
> @@ -380,8 +386,13 @@ static __always_inline bool try_to_steal_lock(struct
> qspinlock *lock, bool parav
>
> iters++;
>
> - if (iters >= get_steal_spins(paravirt))
> + if (iters >= get_steal_spins(paravirt, false))
> break;
> + if (iters >= get_steal_spins(paravirt, true)) {
There's no indication of what true and false mean here which is hard to read.
To me it feels like two separate functions would be more clear.
> + int cpu = get_owner_cpu(val);
> + if (numa_node_id() != cpu_to_node(cpu))
What about using node_distance() instead?
> + break;
> + }
> }
> spin_end();
>
> @@ -588,6 +599,22 @@ static int steal_spins_get(void *data, u64 *val)
>
> DEFINE_SIMPLE_ATTRIBUTE(fops_steal_spins, steal_spins_get, steal_spins_set,
> "%llu\n");
>
> +static int remote_steal_spins_set(void *data, u64 val)
> +{
> + REMOTE_STEAL_SPINS = val;
REMOTE_STEAL_SPINS is int not u64.
> +
> + return 0;
> +}
> +
> +static int remote_steal_spins_get(void *data, u64 *val)
> +{
> + *val = REMOTE_STEAL_SPINS;
> +
> + return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(fops_remote_steal_spins, remote_steal_spins_get,
> remote_steal_spins_set, "%llu\n");
> +
> static int head_spins_set(void *data, u64 val)
> {
> HEAD_SPINS = val;
> @@ -687,6 +714,7 @@ DEFINE_SIMPLE_ATTRIBUTE(fops_pv_prod_head,
> pv_prod_head_get, pv_prod_head_set, "
> static __init int spinlock_debugfs_init(void)
> {
> debugfs_create_file("qspl_steal_spins", 0600, arch_debugfs_dir, NULL,
> &fops_steal_spins);
> + debugfs_create_file("qspl_remote_steal_spins", 0600, arch_debugfs_dir,
> NULL, &fops_remote_steal_spins);
> debugfs_create_file("qspl_head_spins", 0600, arch_debugfs_dir, NULL,
> &fops_head_spins);
> if (is_shared_processor()) {
> debugfs_create_file("qspl_pv_yield_owner", 0600,
> arch_debugfs_dir, NULL, &fops_pv_yield_owner);
