s390/cpumf: introduce AUX buffer for dump diagnostic sample data

Current implementation uses a private buffer for cpumf to dump samples.
Samples first go to this buffer. Then copy to ring buffer allocated
by perf core. With AUX buffer, this copy is not needed. AUX buffer is
shared and zero-copy mapped to user space. The trailer information at
the end of each SDB(sample data block) is also exported to user space.
AUX buffer is used when diagnostic sampling mode is enabled.

This patch contains functions to setup/free AUX buffer or to begin/end
sampling per-cpu. Also include function called in interrupt to
collect samples.

Signed-off-by: Pu Hou <bjhoupu@linux.vnet.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 446 insertions, 0 deletions

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index bd4bbf61aaf3..51dbd8d90dbe 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -77,6 +77,15 @@ struct sf_buffer {
 	unsigned long	 *tail;	    /* last sample-data-block-table */
 };
 
+struct aux_buffer {
+	struct sf_buffer sfb;
+	unsigned long head;	   /* index of SDB of buffer head */
+	unsigned long alert_mark;  /* index of SDB of alert request position */
+	unsigned long empty_mark;  /* mark of SDB not marked full */
+	unsigned long *sdb_index;  /* SDB address for fast lookup */
+	unsigned long *sdbt_index; /* SDBT address for fast lookup */
+};
+
 struct cpu_hw_sf {
 	/* CPU-measurement sampling information block */
 	struct hws_qsi_info_block qsi;
@@ -85,6 +94,7 @@ struct cpu_hw_sf {
 	struct sf_buffer sfb;	    /* Sampling buffer */
 	unsigned int flags;	    /* Status flags */
 	struct perf_event *event;   /* Scheduled perf event */
+	struct perf_output_handle handle; /* AUX buffer output handle */
 };
 static DEFINE_PER_CPU(struct cpu_hw_sf, cpu_hw_sf);
 
@@ -1291,6 +1301,439 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all)
 				    sampl_overflow, event_overflow);
 }
 
+#define AUX_SDB_INDEX(aux, i) ((i) % aux->sfb.num_sdb)
+#define AUX_SDB_NUM(aux, start, end) (end >= start ? end - start + 1 : 0)
+#define AUX_SDB_NUM_ALERT(aux) AUX_SDB_NUM(aux, aux->head, aux->alert_mark)
+#define AUX_SDB_NUM_EMPTY(aux) AUX_SDB_NUM(aux, aux->head, aux->empty_mark)
+
+/*
+ * Get trailer entry by index of SDB.
+ */
+static struct hws_trailer_entry *aux_sdb_trailer(struct aux_buffer *aux,
+						 unsigned long index)
+{
+	unsigned long sdb;
+
+	index = AUX_SDB_INDEX(aux, index);
+	sdb = aux->sdb_index[index];
+	return (struct hws_trailer_entry *)trailer_entry_ptr(sdb);
+}
+
+/*
+ * Finish sampling on the cpu. Called by cpumsf_pmu_del() with pmu
+ * disabled. Collect the full SDBs in AUX buffer which have not reached
+ * the point of alert indicator. And ignore the SDBs which are not
+ * full.
+ *
+ * 1. Scan SDBs to see how much data is there and consume them.
+ * 2. Remove alert indicator in the buffer.
+ */
+static void aux_output_end(struct perf_output_handle *handle)
+{
+	unsigned long i, range_scan, idx;
+	struct aux_buffer *aux;
+	struct hws_trailer_entry *te;
+
+	aux = perf_get_aux(handle);
+	if (!aux)
+		return;
+
+	range_scan = AUX_SDB_NUM_ALERT(aux);
+	for (i = 0, idx = aux->head; i < range_scan; i++, idx++) {
+		te = aux_sdb_trailer(aux, idx);
+		if (!(te->flags & SDB_TE_BUFFER_FULL_MASK))
+			break;
+	}
+	/* i is num of SDBs which are full */
+	perf_aux_output_end(handle, i << PAGE_SHIFT);
+
+	/* Remove alert indicators in the buffer */
+	te = aux_sdb_trailer(aux, aux->alert_mark);
+	te->flags &= ~SDB_TE_ALERT_REQ_MASK;
+
+	debug_sprintf_event(sfdbg, 6, "aux_output_end: collect %lx SDBs\n", i);
+}
+
+/*
+ * Start sampling on the CPU. Called by cpumsf_pmu_add() when an event
+ * is first added to the CPU or rescheduled again to the CPU. It is called
+ * with pmu disabled.
+ *
+ * 1. Reset the trailer of SDBs to get ready for new data.
+ * 2. Tell the hardware where to put the data by reset the SDBs buffer
+ *    head(tear/dear).
+ */
+static int aux_output_begin(struct perf_output_handle *handle,
+			    struct aux_buffer *aux,
+			    struct cpu_hw_sf *cpuhw)
+{
+	unsigned long range;
+	unsigned long i, range_scan, idx;
+	unsigned long head, base, offset;
+	struct hws_trailer_entry *te;
+
+	if (WARN_ON_ONCE(handle->head & ~PAGE_MASK))
+		return -EINVAL;
+
+	aux->head = handle->head >> PAGE_SHIFT;
+	range = (handle->size + 1) >> PAGE_SHIFT;
+	if (range <= 1)
+		return -ENOMEM;
+
+	/*
+	 * SDBs between aux->head and aux->empty_mark are already ready
+	 * for new data. range_scan is num of SDBs not within them.
+	 */
+	if (range > AUX_SDB_NUM_EMPTY(aux)) {
+		range_scan = range - AUX_SDB_NUM_EMPTY(aux);
+		idx = aux->empty_mark + 1;
+		for (i = 0; i < range_scan; i++, idx++) {
+			te = aux_sdb_trailer(aux, idx);
+			te->flags = te->flags & ~SDB_TE_BUFFER_FULL_MASK;
+			te->flags = te->flags & ~SDB_TE_ALERT_REQ_MASK;
+			te->overflow = 0;
+		}
+		/* Save the position of empty SDBs */
+		aux->empty_mark = aux->head + range - 1;
+	}
+
+	/* Set alert indicator */
+	aux->alert_mark = aux->head + range/2 - 1;
+	te = aux_sdb_trailer(aux, aux->alert_mark);
+	te->flags = te->flags | SDB_TE_ALERT_REQ_MASK;
+
+	/* Reset hardware buffer head */
+	head = AUX_SDB_INDEX(aux, aux->head);
+	base = aux->sdbt_index[head / CPUM_SF_SDB_PER_TABLE];
+	offset = head % CPUM_SF_SDB_PER_TABLE;
+	cpuhw->lsctl.tear = base + offset * sizeof(unsigned long);
+	cpuhw->lsctl.dear = aux->sdb_index[head];
+
+	debug_sprintf_event(sfdbg, 6, "aux_output_begin: "
+			    "head->alert_mark->empty_mark (num_alert, range)"
+			    "[%lx -> %lx -> %lx] (%lx, %lx) "
+			    "tear index %lx, tear %lx dear %lx\n",
+			    aux->head, aux->alert_mark, aux->empty_mark,
+			    AUX_SDB_NUM_ALERT(aux), range,
+			    head / CPUM_SF_SDB_PER_TABLE,
+			    cpuhw->lsctl.tear,
+			    cpuhw->lsctl.dear);
+
+	return 0;
+}
+
+/*
+ * Set alert indicator on SDB at index @alert_index while sampler is running.
+ *
+ * Return true if successfully.
+ * Return false if full indicator is already set by hardware sampler.
+ */
+static bool aux_set_alert(struct aux_buffer *aux, unsigned long alert_index,
+			  unsigned long long *overflow)
+{
+	unsigned long long orig_overflow, orig_flags, new_flags;
+	struct hws_trailer_entry *te;
+
+	te = aux_sdb_trailer(aux, alert_index);
+	do {
+		orig_flags = te->flags;
+		orig_overflow = te->overflow;
+		*overflow = orig_overflow;
+		if (orig_flags & SDB_TE_BUFFER_FULL_MASK) {
+			/*
+			 * SDB is already set by hardware.
+			 * Abort and try to set somewhere
+			 * behind.
+			 */
+			return false;
+		}
+		new_flags = orig_flags | SDB_TE_ALERT_REQ_MASK;
+	} while (!cmpxchg_double(&te->flags, &te->overflow,
+				 orig_flags, orig_overflow,
+				 new_flags, 0ULL));
+	return true;
+}
+
+/*
+ * aux_reset_buffer() - Scan and setup SDBs for new samples
+ * @aux:	The AUX buffer to set
+ * @range:	The range of SDBs to scan started from aux->head
+ * @overflow:	Set to overflow count
+ *
+ * Set alert indicator on the SDB at index of aux->alert_mark. If this SDB is
+ * marked as empty, check if it is already set full by the hardware sampler.
+ * If yes, that means new data is already there before we can set an alert
+ * indicator. Caller should try to set alert indicator to some position behind.
+ *
+ * Scan the SDBs in AUX buffer from behind aux->empty_mark. They are used
+ * previously and have already been consumed by user space. Reset these SDBs
+ * (clear full indicator and alert indicator) for new data.
+ * If aux->alert_mark fall in this area, just set it. Overflow count is
+ * recorded while scanning.
+ *
+ * SDBs between aux->head and aux->empty_mark are already reset at last time.
+ * and ready for new samples. So scanning on this area could be skipped.
+ *
+ * Return true if alert indicator is set successfully and false if not.
+ */
+static bool aux_reset_buffer(struct aux_buffer *aux, unsigned long range,
+			     unsigned long long *overflow)
+{
+	unsigned long long orig_overflow, orig_flags, new_flags;
+	unsigned long i, range_scan, idx;
+	struct hws_trailer_entry *te;
+
+	if (range <= AUX_SDB_NUM_EMPTY(aux))
+		/*
+		 * No need to scan. All SDBs in range are marked as empty.
+		 * Just set alert indicator. Should check race with hardware
+		 * sampler.
+		 */
+		return aux_set_alert(aux, aux->alert_mark, overflow);
+
+	if (aux->alert_mark <= aux->empty_mark)
+		/*
+		 * Set alert indicator on empty SDB. Should check race
+		 * with hardware sampler.
+		 */
+		if (!aux_set_alert(aux, aux->alert_mark, overflow))
+			return false;
+
+	/*
+	 * Scan the SDBs to clear full and alert indicator used previously.
+	 * Start scanning from one SDB behind empty_mark. If the new alert
+	 * indicator fall into this range, set it.
+	 */
+	range_scan = range - AUX_SDB_NUM_EMPTY(aux);
+	idx = aux->empty_mark + 1;
+	for (i = 0; i < range_scan; i++, idx++) {
+		te = aux_sdb_trailer(aux, idx);
+		do {
+			orig_flags = te->flags;
+			orig_overflow = te->overflow;
+			new_flags = orig_flags & ~SDB_TE_BUFFER_FULL_MASK;
+			if (idx == aux->alert_mark)
+				new_flags |= SDB_TE_ALERT_REQ_MASK;
+			else
+				new_flags &= ~SDB_TE_ALERT_REQ_MASK;
+		} while (!cmpxchg_double(&te->flags, &te->overflow,
+					 orig_flags, orig_overflow,
+					 new_flags, 0ULL));
+		*overflow += orig_overflow;
+	}
+
+	/* Update empty_mark to new position */
+	aux->empty_mark = aux->head + range - 1;
+
+	return true;
+}
+
+/*
+ * Measurement alert handler for diagnostic mode sampling.
+ */
+static void hw_collect_aux(struct cpu_hw_sf *cpuhw)
+{
+	struct aux_buffer *aux;
+	int done = 0;
+	unsigned long range = 0, size;
+	unsigned long long overflow = 0;
+	struct perf_output_handle *handle = &cpuhw->handle;
+	unsigned long num_sdb;
+
+	aux = perf_get_aux(handle);
+	if (WARN_ON_ONCE(!aux))
+		return;
+
+	/* Inform user space new data arrived */
+	size = AUX_SDB_NUM_ALERT(aux) << PAGE_SHIFT;
+	perf_aux_output_end(handle, size);
+	num_sdb = aux->sfb.num_sdb;
+
+	while (!done) {
+		/* Get an output handle */
+		aux = perf_aux_output_begin(handle, cpuhw->event);
+		if (handle->size == 0) {
+			pr_err("The AUX buffer with %lu pages for the "
+			       "diagnostic-sampling mode is full\n",
+				num_sdb);
+			debug_sprintf_event(sfdbg, 1, "AUX buffer used up\n");
+			break;
+		}
+		if (WARN_ON_ONCE(!aux))
+			return;
+
+		/* Update head and alert_mark to new position */
+		aux->head = handle->head >> PAGE_SHIFT;
+		range = (handle->size + 1) >> PAGE_SHIFT;
+		if (range == 1)
+			aux->alert_mark = aux->head;
+		else
+			aux->alert_mark = aux->head + range/2 - 1;
+
+		if (aux_reset_buffer(aux, range, &overflow)) {
+			if (!overflow) {
+				done = 1;
+				break;
+			}
+			size = range << PAGE_SHIFT;
+			perf_aux_output_end(&cpuhw->handle, size);
+			pr_err("Sample data caused the AUX buffer with %lu "
+			       "pages to overflow\n", num_sdb);
+			debug_sprintf_event(sfdbg, 1, "head %lx range %lx "
+					    "overflow %llx\n",
+					    aux->head, range, overflow);
+		} else {
+			size = AUX_SDB_NUM_ALERT(aux) << PAGE_SHIFT;
+			perf_aux_output_end(&cpuhw->handle, size);
+			debug_sprintf_event(sfdbg, 6, "head %lx alert %lx "
+					    "already full, try another\n",
+					    aux->head, aux->alert_mark);
+		}
+	}
+
+	if (done)
+		debug_sprintf_event(sfdbg, 6, "aux_reset_buffer: "
+				    "[%lx -> %lx -> %lx] (%lx, %lx)\n",
+				    aux->head, aux->alert_mark, aux->empty_mark,
+				    AUX_SDB_NUM_ALERT(aux), range);
+}
+
+/*
+ * Callback when freeing AUX buffers.
+ */
+static void aux_buffer_free(void *data)
+{
+	struct aux_buffer *aux = data;
+	unsigned long i, num_sdbt;
+
+	if (!aux)
+		return;
+
+	/* Free SDBT. SDB is freed by the caller */
+	num_sdbt = aux->sfb.num_sdbt;
+	for (i = 0; i < num_sdbt; i++)
+		free_page(aux->sdbt_index[i]);
+
+	kfree(aux->sdbt_index);
+	kfree(aux->sdb_index);
+	kfree(aux);
+
+	debug_sprintf_event(sfdbg, 4, "aux_buffer_free: free "
+			    "%lu SDBTs\n", num_sdbt);
+}
+
+/*
+ * aux_buffer_setup() - Setup AUX buffer for diagnostic mode sampling
+ * @cpu:	On which to allocate, -1 means current
+ * @pages:	Array of pointers to buffer pages passed from perf core
+ * @nr_pages:	Total pages
+ * @snapshot:	Flag for snapshot mode
+ *
+ * This is the callback when setup an event using AUX buffer. Perf tool can
+ * trigger this by an additional mmap() call on the event. Unlike the buffer
+ * for basic samples, AUX buffer belongs to the event. It is scheduled with
+ * the task among online cpus when it is a per-thread event.
+ *
+ * Return the private AUX buffer structure if success or NULL if fails.
+ */
+static void *aux_buffer_setup(int cpu, void **pages, int nr_pages,
+			      bool snapshot)
+{
+	struct sf_buffer *sfb;
+	struct aux_buffer *aux;
+	unsigned long *new, *tail;
+	int i, n_sdbt;
+
+	if (!nr_pages || !pages)
+		return NULL;
+
+	if (nr_pages > CPUM_SF_MAX_SDB * CPUM_SF_SDB_DIAG_FACTOR) {
+		pr_err("AUX buffer size (%i pages) is larger than the "
+		       "maximum sampling buffer limit\n",
+		       nr_pages);
+		return NULL;
+	} else if (nr_pages < CPUM_SF_MIN_SDB * CPUM_SF_SDB_DIAG_FACTOR) {
+		pr_err("AUX buffer size (%i pages) is less than the "
+		       "minimum sampling buffer limit\n",
+		       nr_pages);
+		return NULL;
+	}
+
+	/* Allocate aux_buffer struct for the event */
+	aux = kmalloc(sizeof(struct aux_buffer), GFP_KERNEL);
+	if (!aux)
+		goto no_aux;
+	sfb = &aux->sfb;
+
+	/* Allocate sdbt_index for fast reference */
+	n_sdbt = (nr_pages + CPUM_SF_SDB_PER_TABLE - 1) / CPUM_SF_SDB_PER_TABLE;
+	aux->sdbt_index = kmalloc_array(n_sdbt, sizeof(void *), GFP_KERNEL);
+	if (!aux->sdbt_index)
+		goto no_sdbt_index;
+
+	/* Allocate sdb_index for fast reference */
+	aux->sdb_index = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL);
+	if (!aux->sdb_index)
+		goto no_sdb_index;
+
+	/* Allocate the first SDBT */
+	sfb->num_sdbt = 0;
+	sfb->sdbt = (unsigned long *) get_zeroed_page(GFP_KERNEL);
+	if (!sfb->sdbt)
+		goto no_sdbt;
+	aux->sdbt_index[sfb->num_sdbt++] = (unsigned long)sfb->sdbt;
+	tail = sfb->tail = sfb->sdbt;
+
+	/*
+	 * Link the provided pages of AUX buffer to SDBT.
+	 * Allocate SDBT if needed.
+	 */
+	for (i = 0; i < nr_pages; i++, tail++) {
+		if (require_table_link(tail)) {
+			new = (unsigned long *) get_zeroed_page(GFP_KERNEL);
+			if (!new)
+				goto no_sdbt;
+			aux->sdbt_index[sfb->num_sdbt++] = (unsigned long)new;
+			/* Link current page to tail of chain */
+			*tail = (unsigned long)(void *) new + 1;
+			tail = new;
+		}
+		/* Tail is the entry in a SDBT */
+		*tail = (unsigned long)pages[i];
+		aux->sdb_index[i] = (unsigned long)pages[i];
+	}
+	sfb->num_sdb = nr_pages;
+
+	/* Link the last entry in the SDBT to the first SDBT */
+	*tail = (unsigned long) sfb->sdbt + 1;
+	sfb->tail = tail;
+
+	/*
+	 * Initial all SDBs are zeroed. Mark it as empty.
+	 * So there is no need to clear the full indicator
+	 * when this event is first added.
+	 */
+	aux->empty_mark = sfb->num_sdb - 1;
+
+	debug_sprintf_event(sfdbg, 4, "aux_buffer_setup: setup %lu SDBTs"
+			    " and %lu SDBs\n",
+			    sfb->num_sdbt, sfb->num_sdb);
+
+	return aux;
+
+no_sdbt:
+	/* SDBs (AUX buffer pages) are freed by caller */
+	for (i = 0; i < sfb->num_sdbt; i++)
+		free_page(aux->sdbt_index[i]);
+	kfree(aux->sdb_index);
+no_sdb_index:
+	kfree(aux->sdbt_index);
+no_sdbt_index:
+	kfree(aux);
+no_aux:
+	return NULL;
+}
+
 static void cpumsf_pmu_read(struct perf_event *event)
 {
 	/* Nothing to do ... updates are interrupt-driven */
@@ -1448,6 +1891,9 @@ static struct pmu cpumf_sampling = {
 	.read	      = cpumsf_pmu_read,
 
 	.attr_groups  = cpumsf_pmu_attr_groups,
+
+	.setup_aux    = aux_buffer_setup,
+	.free_aux     = aux_buffer_free,
 };
 
 static void cpumf_measurement_alert(struct ext_code ext_code,