Commit cc797011 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/qspinlock: reduce remote node steal spins 



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.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221126095932.1234527-15-npiggin@gmail.com
parent 71c23502

arch/powerpc/lib/qspinlock.c

+40 −3
Original line number Diff line number Diff line
@@ -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
@@ -44,6 +46,11 @@ static __always_inline int get_steal_spins(bool paravirt) 
	return steal_spins;

}



static __always_inline int get_remote_steal_spins(bool paravirt)

{

	return remote_steal_spins;

}



static __always_inline int get_head_spins(bool paravirt)

{

	return head_spins;
@@ -335,10 +342,24 @@ static __always_inline void yield_to_prev(struct qspinlock *lock, struct qnode * 
	spin_cpu_relax();

}



static __always_inline bool steal_break(u32 val, int iters, bool paravirt)

{

	if (iters >= get_steal_spins(paravirt))

		return true;



	if (IS_ENABLED(CONFIG_NUMA) &&

	    (iters >= get_remote_steal_spins(paravirt))) {

		int cpu = get_owner_cpu(val);

		if (numa_node_id() != cpu_to_node(cpu))

			return true;

	}

	return false;

}



static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool paravirt)

{

	int iters = 0;

	u32 val;



	if (!steal_spins)

		return false;
@@ -347,8 +368,7 @@ static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool parav 
	spin_begin();



	do {

		u32 val = READ_ONCE(lock->val);



		val = READ_ONCE(lock->val);

		if (val & _Q_MUST_Q_VAL)

			break;
@@ -362,7 +382,7 @@ static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool parav 
		}



		iters++;

	} while (iters < get_steal_spins(paravirt));

	} while (!steal_break(val, iters, paravirt));



	spin_end();
@@ -560,6 +580,22 @@ 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;



	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;
@@ -659,6 +695,7 @@ 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);