diff mbox series

[net-next,2/2] page_pool: Convert page_pool_alloc_stats to u64_stats_t.

Message ID 20250221115221.291006-3-bigeasy@linutronix.de (mailing list archive)
State Not Applicable
Headers show
Series page_pool: Convert stats to u64_stats_t. | expand

Commit Message

Sebastian Andrzej Siewior Feb. 21, 2025, 11:52 a.m. UTC 
Using u64 for statistics can lead to inconsistency on 32bit because an
update and a read requires to access two 32bit values.
This can be avoided by using u64_stats_t for the counters and
u64_stats_sync for the required synchronisation on 32bit platforms. The
synchronisation is a NOP on 64bit architectures.

Use u64_stats_t for the counters in page_pool_recycle_stats.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 .../ethernet/mellanox/mlx5/core/en_stats.c    | 12 ++---
 include/net/page_pool/types.h                 | 14 +++---
 net/core/page_pool.c                          | 45 +++++++++++++------
 net/core/page_pool_user.c                     | 12 ++---
 4 files changed, 52 insertions(+), 31 deletions(-)

Comments

Joe Damato Feb. 21, 2025, 5:30 p.m. UTC | #1 
On Fri, Feb 21, 2025 at 12:52:21PM +0100, Sebastian Andrzej Siewior wrote:
> Using u64 for statistics can lead to inconsistency on 32bit because an
> update and a read requires to access two 32bit values.
> This can be avoided by using u64_stats_t for the counters and
> u64_stats_sync for the required synchronisation on 32bit platforms. The
> synchronisation is a NOP on 64bit architectures.

Same as in previous messages: I'd want to see clearly that this is
indeed an issue on 32bit systems showing before/after assembly.
 
> Use u64_stats_t for the counters in page_pool_recycle_stats.

Commit message says page_pool_recycle_stats, but code below is for
alloc stats.

> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  .../ethernet/mellanox/mlx5/core/en_stats.c    | 12 ++---
>  include/net/page_pool/types.h                 | 14 +++---
>  net/core/page_pool.c                          | 45 +++++++++++++------
>  net/core/page_pool_user.c                     | 12 ++---
>  4 files changed, 52 insertions(+), 31 deletions(-)

[...]

> --- a/include/net/page_pool/types.h
> +++ b/include/net/page_pool/types.h
> @@ -96,6 +96,7 @@ struct page_pool_params {
>  #ifdef CONFIG_PAGE_POOL_STATS
>  /**
>   * struct page_pool_alloc_stats - allocation statistics
> + * @syncp:	synchronisations point for updates.
>   * @fast:	successful fast path allocations
>   * @slow:	slow path order-0 allocations
>   * @slow_high_order: slow path high order allocations
> @@ -105,12 +106,13 @@ struct page_pool_params {
>   *		the cache due to a NUMA mismatch
>   */
>  struct page_pool_alloc_stats {
> -	u64 fast;
> -	u64 slow;
> -	u64 slow_high_order;
> -	u64 empty;
> -	u64 refill;
> -	u64 waive;
> +	struct u64_stats_sync syncp;
> +	u64_stats_t fast;
> +	u64_stats_t slow;
> +	u64_stats_t slow_high_order;
> +	u64_stats_t empty;
> +	u64_stats_t refill;
> +	u64_stats_t waive;
>  };

When I tried to get this in initially, Jesper had feelings about the
cacheline placement of the counters. I have no idea if that is still
the case or not.

My suggestion to you (assuming that your initial assertion is
correct that this_cpu_inc isn't safe on 32bit x86) would be to:

  - include pahole output showing the placement of these counters
  - include the same benchmarks I included in the original series
    [1] that Jesper requested from me. I believe the code for the
    benchmarks can be found here:
       https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/lib

That would probably make it easier for the page pool people to
review / ack and would likely result in fewer revisions.

[1]: https://lore.kernel.org/all/1646172610-129397-1-git-send-email-jdamato@fastly.com/
diff mbox series

Patch

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c b/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
index baff961970f25..afb5c135b68c1 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_stats.c
@@ -506,12 +506,12 @@  static void mlx5e_stats_update_stats_rq_page_pool(struct mlx5e_channel *c)
 	if (!page_pool_get_stats(pool, &stats))
 		return;
 
-	rq_stats->pp_alloc_fast = stats.alloc_stats.fast;
-	rq_stats->pp_alloc_slow = stats.alloc_stats.slow;
-	rq_stats->pp_alloc_slow_high_order = stats.alloc_stats.slow_high_order;
-	rq_stats->pp_alloc_empty = stats.alloc_stats.empty;
-	rq_stats->pp_alloc_waive = stats.alloc_stats.waive;
-	rq_stats->pp_alloc_refill = stats.alloc_stats.refill;
+	rq_stats->pp_alloc_fast = u64_stats_read(&stats.alloc_stats.fast);
+	rq_stats->pp_alloc_slow = u64_stats_read(&stats.alloc_stats.slow);
+	rq_stats->pp_alloc_slow_high_order = u64_stats_read(&stats.alloc_stats.slow_high_order);
+	rq_stats->pp_alloc_empty = u64_stats_read(&stats.alloc_stats.empty);
+	rq_stats->pp_alloc_waive = u64_stats_read(&stats.alloc_stats.waive);
+	rq_stats->pp_alloc_refill = u64_stats_read(&stats.alloc_stats.refill);
 
 	rq_stats->pp_recycle_cached = u64_stats_read(&stats.recycle_stats.cached);
 	rq_stats->pp_recycle_cache_full = u64_stats_read(&stats.recycle_stats.cache_full);
diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
index c5ad80a542b7d..f45d55e6e8643 100644
--- a/include/net/page_pool/types.h
+++ b/include/net/page_pool/types.h
@@ -96,6 +96,7 @@  struct page_pool_params {
 #ifdef CONFIG_PAGE_POOL_STATS
 /**
  * struct page_pool_alloc_stats - allocation statistics
+ * @syncp:	synchronisations point for updates.
  * @fast:	successful fast path allocations
  * @slow:	slow path order-0 allocations
  * @slow_high_order: slow path high order allocations
@@ -105,12 +106,13 @@  struct page_pool_params {
  *		the cache due to a NUMA mismatch
  */
 struct page_pool_alloc_stats {
-	u64 fast;
-	u64 slow;
-	u64 slow_high_order;
-	u64 empty;
-	u64 refill;
-	u64 waive;
+	struct u64_stats_sync syncp;
+	u64_stats_t fast;
+	u64_stats_t slow;
+	u64_stats_t slow_high_order;
+	u64_stats_t empty;
+	u64_stats_t refill;
+	u64_stats_t waive;
 };
 
 /**
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 36fa14a1e8441..d69a03609613b 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -42,7 +42,14 @@  static DEFINE_PER_CPU(struct page_pool_recycle_stats, pp_system_recycle_stats) =
 };
 
 /* alloc_stat_inc is intended to be used in softirq context */
-#define alloc_stat_inc(pool, __stat)	(pool->alloc_stats.__stat++)
+#define alloc_stat_inc(pool, __stat)						\
+	do {									\
+		struct page_pool_alloc_stats *s = &pool->alloc_stats;		\
+		u64_stats_update_begin(&s->syncp);				\
+		u64_stats_inc(&s->__stat);					\
+		u64_stats_update_end(&s->syncp);				\
+	} while (0)
+
 /* recycle_stat_inc is safe to use when preemption is possible. */
 #define recycle_stat_inc(pool, __stat)							\
 	do {										\
@@ -88,19 +95,30 @@  static const char pp_stats[][ETH_GSTRING_LEN] = {
 bool page_pool_get_stats(const struct page_pool *pool,
 			 struct page_pool_stats *stats)
 {
+	const struct page_pool_alloc_stats *alloc_stats;
 	unsigned int start;
 	int cpu = 0;
 
 	if (!stats)
 		return false;
 
+	alloc_stats = &pool->alloc_stats;
 	/* The caller is responsible to initialize stats. */
-	stats->alloc_stats.fast += pool->alloc_stats.fast;
-	stats->alloc_stats.slow += pool->alloc_stats.slow;
-	stats->alloc_stats.slow_high_order += pool->alloc_stats.slow_high_order;
-	stats->alloc_stats.empty += pool->alloc_stats.empty;
-	stats->alloc_stats.refill += pool->alloc_stats.refill;
-	stats->alloc_stats.waive += pool->alloc_stats.waive;
+	do {
+		start = u64_stats_fetch_begin(&alloc_stats->syncp);
+		u64_stats_add(&stats->alloc_stats.fast,
+			      u64_stats_read(&alloc_stats->fast));
+		u64_stats_add(&stats->alloc_stats.slow,
+			      u64_stats_read(&alloc_stats->slow));
+		u64_stats_add(&stats->alloc_stats.slow_high_order,
+			      u64_stats_read(&alloc_stats->slow_high_order));
+		u64_stats_add(&stats->alloc_stats.empty,
+			      u64_stats_read(&alloc_stats->empty));
+		u64_stats_add(&stats->alloc_stats.refill,
+			      u64_stats_read(&alloc_stats->refill));
+		u64_stats_add(&stats->alloc_stats.waive,
+			      u64_stats_read(&alloc_stats->waive));
+	} while (u64_stats_fetch_retry(&alloc_stats->syncp, start));
 
 	for_each_possible_cpu(cpu) {
 		const struct page_pool_recycle_stats *pcpu =
@@ -148,12 +166,12 @@  u64 *page_pool_ethtool_stats_get(u64 *data, const void *stats)
 {
 	const struct page_pool_stats *pool_stats = stats;
 
-	*data++ = pool_stats->alloc_stats.fast;
-	*data++ = pool_stats->alloc_stats.slow;
-	*data++ = pool_stats->alloc_stats.slow_high_order;
-	*data++ = pool_stats->alloc_stats.empty;
-	*data++ = pool_stats->alloc_stats.refill;
-	*data++ = pool_stats->alloc_stats.waive;
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.fast);
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.slow);
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.slow_high_order);
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.empty);
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.refill);
+	*data++ = u64_stats_read(&pool_stats->alloc_stats.waive);
 	*data++ = u64_stats_read(&pool_stats->recycle_stats.cached);
 	*data++ = u64_stats_read(&pool_stats->recycle_stats.cache_full);
 	*data++ = u64_stats_read(&pool_stats->recycle_stats.ring);
@@ -278,6 +296,7 @@  static int page_pool_init(struct page_pool *pool,
 		pool->recycle_stats = &pp_system_recycle_stats;
 		pool->system = true;
 	}
+	u64_stats_init(&pool->alloc_stats.syncp);
 #endif
 
 	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0) {
diff --git a/net/core/page_pool_user.c b/net/core/page_pool_user.c
index 0d038c0c8996d..c368cb141147f 100644
--- a/net/core/page_pool_user.c
+++ b/net/core/page_pool_user.c
@@ -137,17 +137,17 @@  page_pool_nl_stats_fill(struct sk_buff *rsp, const struct page_pool *pool,
 	nla_nest_end(rsp, nest);
 
 	if (nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_FAST,
-			 stats.alloc_stats.fast) ||
+			 u64_stats_read(&stats.alloc_stats.fast)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_SLOW,
-			 stats.alloc_stats.slow) ||
+			 u64_stats_read(&stats.alloc_stats.slow)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_SLOW_HIGH_ORDER,
-			 stats.alloc_stats.slow_high_order) ||
+			 u64_stats_read(&stats.alloc_stats.slow_high_order)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_EMPTY,
-			 stats.alloc_stats.empty) ||
+			 u64_stats_read(&stats.alloc_stats.empty)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_REFILL,
-			 stats.alloc_stats.refill) ||
+			 u64_stats_read(&stats.alloc_stats.refill)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_ALLOC_WAIVE,
-			 stats.alloc_stats.waive) ||
+			 u64_stats_read(&stats.alloc_stats.waive)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_RECYCLE_CACHED,
 			 u64_stats_read(&stats.recycle_stats.cached)) ||
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_STATS_RECYCLE_CACHE_FULL,