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Message-Id: <20240802004308.4134731-9-paulmck@kernel.org>
Date: Thu, 1 Aug 2024 17:43:06 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
kernel-team@...a.com,
rostedt@...dmis.org,
"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 09/11] rcuscale: Use special allocator for rcu_scale_writer()
The rcu_scale_writer() function needs only a fixed number of rcu_head
structures per kthread, which means that a trivial allocator suffices.
This commit therefore uses an llist-based allocator using a fixed array of
structures per kthread. This allows aggressive testing of RCU performance
without stressing the slab allocators.
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
kernel/rcu/rcuscale.c | 123 ++++++++++++++++++++++++++++++++++++++----
1 file changed, 113 insertions(+), 10 deletions(-)
diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 01d48eb753b41..f945f8175e859 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -105,6 +105,19 @@ static char *scale_type = "rcu";
module_param(scale_type, charp, 0444);
MODULE_PARM_DESC(scale_type, "Type of RCU to scalability-test (rcu, srcu, ...)");
+// Structure definitions for custom fixed-per-task allocator.
+struct writer_mblock {
+ struct rcu_head wmb_rh;
+ struct llist_node wmb_node;
+ struct writer_freelist *wmb_wfl;
+};
+
+struct writer_freelist {
+ struct llist_head ws_lhg;
+ struct llist_head ____cacheline_internodealigned_in_smp ws_lhp;
+ struct writer_mblock *ws_mblocks;
+};
+
static int nrealreaders;
static int nrealwriters;
static struct task_struct **writer_tasks;
@@ -113,6 +126,7 @@ static struct task_struct *shutdown_task;
static u64 **writer_durations;
static bool *writer_done;
+static struct writer_freelist *writer_freelists;
static int *writer_n_durations;
static atomic_t n_rcu_scale_reader_started;
static atomic_t n_rcu_scale_writer_started;
@@ -463,13 +477,52 @@ rcu_scale_reader(void *arg)
return 0;
}
+/*
+ * Allocate a writer_mblock structure for the specified rcu_scale_writer
+ * task.
+ */
+static struct writer_mblock *rcu_scale_alloc(long me)
+{
+ struct llist_node *llnp;
+ struct writer_freelist *wflp;
+ struct writer_mblock *wmbp;
+
+ if (WARN_ON_ONCE(!writer_freelists))
+ return NULL;
+ wflp = &writer_freelists[me];
+ if (llist_empty(&wflp->ws_lhp)) {
+ // ->ws_lhp is private to its rcu_scale_writer task.
+ wmbp = container_of(llist_del_all(&wflp->ws_lhg), struct writer_mblock, wmb_node);
+ wflp->ws_lhp.first = &wmbp->wmb_node;
+ }
+ llnp = llist_del_first(&wflp->ws_lhp);
+ if (!llnp)
+ return NULL;
+ return container_of(llnp, struct writer_mblock, wmb_node);
+}
+
+/*
+ * Free a writer_mblock structure to its rcu_scale_writer task.
+ */
+static void rcu_scale_free(struct writer_mblock *wmbp)
+{
+ struct writer_freelist *wflp;
+
+ if (!wmbp)
+ return;
+ wflp = wmbp->wmb_wfl;
+ llist_add(&wmbp->wmb_node, &wflp->ws_lhg);
+}
+
/*
* Callback function for asynchronous grace periods from rcu_scale_writer().
*/
static void rcu_scale_async_cb(struct rcu_head *rhp)
{
+ struct writer_mblock *wmbp = container_of(rhp, struct writer_mblock, wmb_rh);
+
atomic_dec(this_cpu_ptr(&n_async_inflight));
- kfree(rhp);
+ rcu_scale_free(wmbp);
}
/*
@@ -482,13 +535,13 @@ rcu_scale_writer(void *arg)
int i_max;
unsigned long jdone;
long me = (long)arg;
- struct rcu_head *rhp = NULL;
bool selfreport = false;
bool started = false, done = false, alldone = false;
u64 t;
DEFINE_TORTURE_RANDOM(tr);
u64 *wdp;
u64 *wdpp = writer_durations[me];
+ struct writer_mblock *wmbp = NULL;
VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started");
WARN_ON(!wdpp);
@@ -529,17 +582,18 @@ rcu_scale_writer(void *arg)
wdp = &wdpp[i];
*wdp = ktime_get_mono_fast_ns();
if (gp_async && !WARN_ON_ONCE(!cur_ops->async)) {
- if (!rhp)
- rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
- if (rhp && atomic_read(this_cpu_ptr(&n_async_inflight)) < gp_async_max) {
+ if (!wmbp)
+ wmbp = rcu_scale_alloc(me);
+ if (wmbp && atomic_read(this_cpu_ptr(&n_async_inflight)) < gp_async_max) {
atomic_inc(this_cpu_ptr(&n_async_inflight));
- cur_ops->async(rhp, rcu_scale_async_cb);
- rhp = NULL;
+ cur_ops->async(&wmbp->wmb_rh, rcu_scale_async_cb);
+ wmbp = NULL;
gp_succeeded = true;
} else if (!kthread_should_stop()) {
cur_ops->gp_barrier();
} else {
- kfree(rhp); /* Because we are stopping. */
+ rcu_scale_free(wmbp); /* Because we are stopping. */
+ wmbp = NULL;
}
} else if (gp_exp) {
cur_ops->exp_sync();
@@ -607,6 +661,7 @@ rcu_scale_writer(void *arg)
rcu_scale_wait_shutdown();
} while (!torture_must_stop());
if (gp_async && cur_ops->async) {
+ rcu_scale_free(wmbp);
cur_ops->gp_barrier();
}
writer_n_durations[me] = i_max + 1;
@@ -970,10 +1025,28 @@ rcu_scale_cleanup(void)
schedule_timeout_uninterruptible(1);
}
kfree(writer_durations[i]);
+ if (writer_freelists) {
+ int ctr = 0;
+ struct llist_node *llnp;
+ struct writer_freelist *wflp = &writer_freelists[i];
+
+ if (wflp->ws_mblocks) {
+ llist_for_each(llnp, wflp->ws_lhg.first)
+ ctr++;
+ llist_for_each(llnp, wflp->ws_lhp.first)
+ ctr++;
+ WARN_ONCE(ctr != gp_async_max,
+ "%s: ctr = %d gp_async_max = %d\n",
+ __func__, ctr, gp_async_max);
+ kfree(wflp->ws_mblocks);
+ }
+ }
}
kfree(writer_tasks);
kfree(writer_durations);
kfree(writer_n_durations);
+ kfree(writer_freelists);
+ writer_freelists = NULL;
}
/* Do torture-type-specific cleanup operations. */
@@ -1000,8 +1073,9 @@ rcu_scale_shutdown(void *arg)
static int __init
rcu_scale_init(void)
{
- long i;
int firsterr = 0;
+ long i;
+ long j;
static struct rcu_scale_ops *scale_ops[] = {
&rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
};
@@ -1072,7 +1146,18 @@ rcu_scale_init(void)
writer_durations = kcalloc(nrealwriters, sizeof(*writer_durations), GFP_KERNEL);
writer_n_durations = kcalloc(nrealwriters, sizeof(*writer_n_durations), GFP_KERNEL);
writer_done = kcalloc(nrealwriters, sizeof(writer_done[0]), GFP_KERNEL);
- if (!writer_tasks || !writer_durations || !writer_n_durations || !writer_done) {
+ if (gp_async) {
+ if (gp_async_max <= 0) {
+ pr_warn("%s: gp_async_max = %d must be greater than zero.\n",
+ __func__, gp_async_max);
+ WARN_ON_ONCE(IS_BUILTIN(CONFIG_RCU_TORTURE_TEST));
+ firsterr = -EINVAL;
+ goto unwind;
+ }
+ writer_freelists = kcalloc(nrealwriters, sizeof(writer_freelists[0]), GFP_KERNEL);
+ }
+ if (!writer_tasks || !writer_durations || !writer_n_durations || !writer_done ||
+ (gp_async && !writer_freelists)) {
SCALEOUT_ERRSTRING("out of memory");
firsterr = -ENOMEM;
goto unwind;
@@ -1085,6 +1170,24 @@ rcu_scale_init(void)
firsterr = -ENOMEM;
goto unwind;
}
+ if (writer_freelists) {
+ struct writer_freelist *wflp = &writer_freelists[i];
+
+ init_llist_head(&wflp->ws_lhg);
+ init_llist_head(&wflp->ws_lhp);
+ wflp->ws_mblocks = kcalloc(gp_async_max, sizeof(wflp->ws_mblocks[0]),
+ GFP_KERNEL);
+ if (!wflp->ws_mblocks) {
+ firsterr = -ENOMEM;
+ goto unwind;
+ }
+ for (j = 0; j < gp_async_max; j++) {
+ struct writer_mblock *wmbp = &wflp->ws_mblocks[j];
+
+ wmbp->wmb_wfl = wflp;
+ llist_add(&wmbp->wmb_node, &wflp->ws_lhp);
+ }
+ }
firsterr = torture_create_kthread(rcu_scale_writer, (void *)i,
writer_tasks[i]);
if (torture_init_error(firsterr))
--
2.40.1
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