Re: [PATCH 7/8] powerpc/perf/hv-24x7: Support v2 of the hypervisor API

[Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>]

Hello Suka,

Thanks for your review!

Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
> Thiago Jung Bauermann [bauerman@linux.vnet.ibm.com] wrote:
>> @@ -166,9 +174,12 @@ DEFINE_PER_CPU(struct hv_24x7_hw, hv_24x7_hw);
>>  DEFINE_PER_CPU(char, hv_24x7_reqb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
>>  DEFINE_PER_CPU(char, hv_24x7_resb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
>> 
>> -#define MAX_NUM_REQUESTS	((H24x7_DATA_BUFFER_SIZE -		       \
>> +#define MAX_NUM_REQUESTS_V1	((H24x7_DATA_BUFFER_SIZE -		       \
>> +					sizeof(struct hv_24x7_request_buffer)) \
>> +					/ H24x7_REQUEST_SIZE_V1)
>> +#define MAX_NUM_REQUESTS_V2	((H24x7_DATA_BUFFER_SIZE -		       \
>>  					sizeof(struct hv_24x7_request_buffer)) \
>> -					/ sizeof(struct hv_24x7_request))
>> +					/ H24x7_REQUEST_SIZE_V2)
>
> Nit: Can we define MAX_NUM_REQUESTS(version) - with a version parameter ? It
> will...

That's a good idea. I created a function instead of a macro, I think it
makes the code clearer since the macro would be a bit harder to read.

>> @@ -1101,9 +1112,13 @@ static int add_event_to_24x7_request(struct perf_event *event,
>>  {
>>  	u16 idx;
>>  	int i;
>> +	size_t req_size;
>>  	struct hv_24x7_request *req;
>> 
>> -	if (request_buffer->num_requests >= MAX_NUM_REQUESTS) {
>> +	if ((request_buffer->interface_version == 1
>> +	     && request_buffer->num_requests >= MAX_NUM_REQUESTS_V1)
>> +	    || (request_buffer->interface_version > 1
>> +		&& request_buffer->num_requests >= MAX_NUM_REQUESTS_V2)) {
>>  		pr_devel("Too many requests for 24x7 HCALL %d\n",
>
> ...simplify this check to
>
> 	if (request->buffer->num_requests >= MAX_NUM_REQUESTS(version))

That's better indeed.

>>  				request_buffer->num_requests);
>>  		return -EINVAL;
>> @@ -1120,8 +1135,11 @@ static int add_event_to_24x7_request(struct perf_event *event,
>>  		idx = event_get_vcpu(event);
>>  	}
>> 
>> +	req_size = request_buffer->interface_version == 1 ?
>> +			   H24x7_REQUEST_SIZE_V1 : H24x7_REQUEST_SIZE_V2;
>> +
>
> Maybe similarly, with H24x7_REQUEST_SIZE(version) ?

I implement this suggestion too.

>> +/**
>> + * get_count_from_result - get event count from the given result
>> + *
>> + * @event:	Event associated with @res.
>> + * @resb:	Result buffer containing @res.
>> + * @res:	Result to work on.
>> + * @countp:	Output variable containing the event count.
>> + * @next:	Optional output variable pointing to the next result in @resb.
>> + */
>> +static int get_count_from_result(struct perf_event *event,
>> +				 struct hv_24x7_data_result_buffer *resb,
>> +				 struct hv_24x7_result *res, u64 *countp,
>> +				 struct hv_24x7_result **next)
>> +{
>> +	u16 num_elements = be16_to_cpu(res->num_elements_returned);
>> +	u16 data_size = be16_to_cpu(res->result_element_data_size);
>> +	unsigned int data_offset;
>> +	void *element_data;
>> +	int ret = 0;
>> +
>> +	/*
>> +	 * We can bail out early if the result is empty.
>> +	 */
>> +	if (!num_elements) {
>> +		pr_debug("Result of request %hhu is empty, nothing to do\n",
>> +			 res->result_ix);
>> +
>> +		if (next)
>> +			*next = (struct hv_24x7_result *) res->elements;
>> +
>> +		return -ENODATA;
>> +	}
>> +
>> +	/*
>> +	 * This code assumes that a result has only one element.
>> +	 */
>> +	if (num_elements != 1) {
>> +		pr_debug("Error: result of request %hhu has %hu elements\n",
>> +			 res->result_ix, num_elements);
>
> Could this happen due to an user request or would this indicate a bug
> in the way we submitted the request (perf should submit separate request
> for each lpar/index - we set ->max_ix and ->max_num_lpars to cpu_be16(1).

That's a good question. I don't know to be honest.

> Minor inconsistency with proceeding, is that if the next element passes,
> this return code is lost/over written. IOW, h_24x7_event_commit_txn()'s
> return value depends on the last element we process, even if intermediate
> ones encounter an error.

Good point. Would it be better if h_24x7_event_commit_txn interrupted
processing and returned an error instead of continuing?

The version below addresses your comments, except the one above.

Subject: [PATCH 7/8] powerpc/perf/hv-24x7: Support v2 of the hypervisor API

POWER9 introduces a new version of the hypervisor API to access the 24x7
perf counters. The new version changed some of the structures used for
requests and results.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
 arch/powerpc/perf/hv-24x7.c            | 143 +++++++++++++++++++++++++++------
 arch/powerpc/perf/hv-24x7.h            |  58 ++++++++++---
 arch/powerpc/platforms/pseries/Kconfig |   2 +-
 3 files changed, 169 insertions(+), 34 deletions(-)

diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index 043cbc78be98..35010403f191 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 
+#include <asm/cputhreads.h>
 #include <asm/firmware.h>
 #include <asm/hvcall.h>
 #include <asm/io.h>
@@ -27,6 +28,9 @@
 #include "hv-24x7-catalog.h"
 #include "hv-common.h"
 
+/* Version of the 24x7 hypervisor API that we should use in this machine. */
+static int interface_version;
+
 static bool domain_is_valid(unsigned domain)
 {
 	switch (domain) {
@@ -74,7 +78,11 @@ static const char *domain_name(unsigned domain)
 
 static bool catalog_entry_domain_is_valid(unsigned domain)
 {
-	return is_physical_domain(domain);
+	/* POWER8 doesn't support virtual domains. */
+	if (interface_version == 1)
+		return is_physical_domain(domain);
+	else
+		return domain_is_valid(domain);
 }
 
 /*
@@ -166,9 +174,11 @@ DEFINE_PER_CPU(struct hv_24x7_hw, hv_24x7_hw);
 DEFINE_PER_CPU(char, hv_24x7_reqb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
 DEFINE_PER_CPU(char, hv_24x7_resb[H24x7_DATA_BUFFER_SIZE]) __aligned(4096);
 
-#define MAX_NUM_REQUESTS	((H24x7_DATA_BUFFER_SIZE -		       \
-					sizeof(struct hv_24x7_request_buffer)) \
-					/ sizeof(struct hv_24x7_request))
+static unsigned int max_num_requests(int interface_version)
+{
+	return (H24x7_DATA_BUFFER_SIZE - sizeof(struct hv_24x7_request_buffer))
+		/ H24x7_REQUEST_SIZE(interface_version);
+}
 
 static char *event_name(struct hv_24x7_event_data *ev, int *len)
 {
@@ -1052,7 +1062,7 @@ static void init_24x7_request(struct hv_24x7_request_buffer *request_buffer,
 	memset(request_buffer, 0, H24x7_DATA_BUFFER_SIZE);
 	memset(result_buffer, 0, H24x7_DATA_BUFFER_SIZE);
 
-	request_buffer->interface_version = HV_24X7_IF_VERSION_CURRENT;
+	request_buffer->interface_version = interface_version;
 	/* memset above set request_buffer->num_requests to 0 */
 }
 
@@ -1077,7 +1087,7 @@ static int make_24x7_request(struct hv_24x7_request_buffer *request_buffer,
 	if (ret) {
 		struct hv_24x7_request *req;
 
-		req = &request_buffer->requests[0];
+		req = request_buffer->requests;
 		pr_notice_ratelimited("hcall failed: [%d %#x %#x %d] => ret 0x%lx (%ld) detail=0x%x failing ix=%x\n",
 				      req->performance_domain, req->data_offset,
 				      req->starting_ix, req->starting_lpar_ix,
@@ -1101,9 +1111,11 @@ static int add_event_to_24x7_request(struct perf_event *event,
 {
 	u16 idx;
 	int i;
+	size_t req_size;
 	struct hv_24x7_request *req;
 
-	if (request_buffer->num_requests >= MAX_NUM_REQUESTS) {
+	if (request_buffer->num_requests >=
+	    max_num_requests(request_buffer->interface_version)) {
 		pr_devel("Too many requests for 24x7 HCALL %d\n",
 				request_buffer->num_requests);
 		return -EINVAL;
@@ -1120,8 +1132,10 @@ static int add_event_to_24x7_request(struct perf_event *event,
 		idx = event_get_vcpu(event);
 	}
 
+	req_size = H24x7_REQUEST_SIZE(request_buffer->interface_version);
+
 	i = request_buffer->num_requests++;
-	req = &request_buffer->requests[i];
+	req = (void *) request_buffer->requests + i * req_size;
 
 	req->performance_domain = event_get_domain(event);
 	req->data_size = cpu_to_be16(8);
@@ -1131,14 +1145,97 @@ static int add_event_to_24x7_request(struct perf_event *event,
 	req->starting_ix = cpu_to_be16(idx);
 	req->max_ix = cpu_to_be16(1);
 
+	if (request_buffer->interface_version > 1 &&
+	    req->performance_domain != HV_PERF_DOMAIN_PHYS_CHIP) {
+		req->starting_thread_group_ix = idx % 2;
+		req->max_num_thread_groups = 1;
+	}
+
 	return 0;
 }
 
+/**
+ * get_count_from_result - get event count from the given result
+ *
+ * @event:	Event associated with @res.
+ * @resb:	Result buffer containing @res.
+ * @res:	Result to work on.
+ * @countp:	Output variable containing the event count.
+ * @next:	Optional output variable pointing to the next result in @resb.
+ */
+static int get_count_from_result(struct perf_event *event,
+				 struct hv_24x7_data_result_buffer *resb,
+				 struct hv_24x7_result *res, u64 *countp,
+				 struct hv_24x7_result **next)
+{
+	u16 num_elements = be16_to_cpu(res->num_elements_returned);
+	u16 data_size = be16_to_cpu(res->result_element_data_size);
+	unsigned int data_offset;
+	void *element_data;
+	int ret = 0;
+
+	/*
+	 * We can bail out early if the result is empty.
+	 */
+	if (!num_elements) {
+		pr_debug("Result of request %hhu is empty, nothing to do\n",
+			 res->result_ix);
+
+		if (next)
+			*next = (struct hv_24x7_result *) res->elements;
+
+		return -ENODATA;
+	}
+
+	/*
+	 * This code assumes that a result has only one element.
+	 */
+	if (num_elements != 1) {
+		pr_debug("Error: result of request %hhu has %hu elements\n",
+			 res->result_ix, num_elements);
+
+		if (!next)
+			return -ENOTSUPP;
+
+		/*
+		 * We still need to go through the motions so that we can return
+		 * a pointer to the next result.
+		 */
+		ret = -ENOTSUPP;
+	}
+
+	if (data_size != sizeof(u64)) {
+		pr_debug("Error: result of request %hhu has data of %hu bytes\n",
+			 res->result_ix, data_size);
+
+		if (!next)
+			return -ENOTSUPP;
+
+		ret = -ENOTSUPP;
+	}
+
+	if (resb->interface_version == 1)
+		data_offset = offsetof(struct hv_24x7_result_element_v1,
+				       element_data);
+	else
+		data_offset = offsetof(struct hv_24x7_result_element_v2,
+				       element_data);
+
+	element_data = res->elements + data_offset;
+
+	if (!ret)
+		*countp = be64_to_cpu(*((u64 *) element_data));
+
+	/* The next result is after the result element. */
+	if (next)
+		*next = element_data + data_size;
+
+	return ret;
+}
+
 static int single_24x7_request(struct perf_event *event, u64 *count)
 {
 	int ret;
-	u16 num_elements;
-	struct hv_24x7_result *result;
 	struct hv_24x7_request_buffer *request_buffer;
 	struct hv_24x7_data_result_buffer *result_buffer;
 
@@ -1158,14 +1255,9 @@ static int single_24x7_request(struct perf_event *event, u64 *count)
 	if (ret)
 		goto out;
 
-	result = result_buffer->results;
-
-	/* This code assumes that a result has only one element. */
-	num_elements = be16_to_cpu(result->num_elements_returned);
-	WARN_ON_ONCE(num_elements != 1);
-
 	/* process result from hcall */
-	*count = be64_to_cpu(result->elements[0].element_data[0]);
+	ret = get_count_from_result(event, result_buffer,
+				    result_buffer->results, count, NULL);
 
 out:
 	put_cpu_var(hv_24x7_reqb);
@@ -1425,16 +1517,13 @@ static int h_24x7_event_commit_txn(struct pmu *pmu)
 	for (i = 0, res = result_buffer->results;
 	     i < result_buffer->num_results; i++, res = next_res) {
 		struct perf_event *event = h24x7hw->events[res->result_ix];
-		u16 num_elements = be16_to_cpu(res->num_elements_returned);
-		u16 data_size = be16_to_cpu(res->result_element_data_size);
 
-		/* This code assumes that a result has only one element. */
-		WARN_ON_ONCE(num_elements != 1);
+		ret = get_count_from_result(event, result_buffer, res, &count,
+					    &next_res);
+		if (ret)
+			continue;
 
-		count = be64_to_cpu(res->elements[0].element_data[0]);
 		update_event_count(event, count);
-
-		next_res = (void *) res->elements[0].element_data + data_size;
 	}
 
 	put_cpu_var(hv_24x7_hw);
@@ -1486,6 +1575,12 @@ static int hv_24x7_init(void)
 		return -ENODEV;
 	}
 
+	/* POWER8 only supports v1, while POWER9 only supports v2. */
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		interface_version = 2;
+	else
+		interface_version = 1;
+
 	hret = hv_perf_caps_get(&caps);
 	if (hret) {
 		pr_debug("could not obtain capabilities, not enabling, rc=%ld\n",
diff --git a/arch/powerpc/perf/hv-24x7.h b/arch/powerpc/perf/hv-24x7.h
index b95909400b2a..5092c4a222a6 100644
--- a/arch/powerpc/perf/hv-24x7.h
+++ b/arch/powerpc/perf/hv-24x7.h
@@ -10,6 +10,8 @@ enum hv_perf_domains {
 	HV_PERF_DOMAIN_MAX,
 };
 
+#define H24x7_REQUEST_SIZE(iface_version)	(iface_version == 1 ? 16 : 32)
+
 struct hv_24x7_request {
 	/* PHYSICAL domains require enabling via phyp/hmc. */
 	__u8 performance_domain;
@@ -42,19 +44,47 @@ struct hv_24x7_request {
 	/* chip, core, or virtual processor based on @performance_domain */
 	__be16 starting_ix;
 	__be16 max_ix;
+
+	/* The following fields were added in v2 of the 24x7 interface. */
+
+	__u8 starting_thread_group_ix;
+
+	/* -1 means all thread groups starting at @starting_thread_group_ix */
+	__u8 max_num_thread_groups;
+
+	__u8 reserved2[0xE];
 } __packed;
 
 struct hv_24x7_request_buffer {
 	/* 0 - ? */
 	/* 1 - ? */
-#define HV_24X7_IF_VERSION_CURRENT 0x01
 	__u8 interface_version;
 	__u8 num_requests;
 	__u8 reserved[0xE];
-	struct hv_24x7_request requests[1];
+	struct hv_24x7_request requests[];
+} __packed;
+
+struct hv_24x7_result_element_v1 {
+	__be16 lpar_ix;
+
+	/*
+	 * represents the core, chip, or virtual processor based on the
+	 * request's @performance_domain
+	 */
+	__be16 domain_ix;
+
+	/* -1 if @performance_domain does not refer to a virtual processor */
+	__be32 lpar_cfg_instance_id;
+
+	/* size = @result_element_data_size of containing result. */
+	__u64 element_data[];
 } __packed;
 
-struct hv_24x7_result_element {
+/*
+ * We need a separate struct for v2 because the offset of @element_data changed
+ * between versions.
+ */
+struct hv_24x7_result_element_v2 {
 	__be16 lpar_ix;
 
 	/*
@@ -66,8 +96,12 @@ struct hv_24x7_result_element {
 	/* -1 if @performance_domain does not refer to a virtual processor */
 	__be32 lpar_cfg_instance_id;
 
+	__u8 thread_group_ix;
+
+	__u8 reserved[7];
+
 	/* size = @result_element_data_size of containing result. */
-	__u64 element_data[1];
+	__u64 element_data[];
 } __packed;
 
 struct hv_24x7_result {
@@ -94,10 +128,16 @@ struct hv_24x7_result {
 	__be16 result_element_data_size;
 	__u8 reserved[0x2];
 
-	/* WARNING: only valid for first result element due to variable sizes
-	 *          of result elements */
-	/* struct hv_24x7_result_element[@num_elements_returned] */
-	struct hv_24x7_result_element elements[1];
+	/*
+	 * Either
+	 *	struct hv_24x7_result_element_v1[@num_elements_returned]
+	 * or
+	 *	struct hv_24x7_result_element_v2[@num_elements_returned]
+	 *
+	 * depending on the interface_version field of the
+	 * struct hv_24x7_data_result_buffer containing this result.
+	 */
+	char elements[];
 } __packed;
 
 struct hv_24x7_data_result_buffer {
@@ -113,7 +153,7 @@ struct hv_24x7_data_result_buffer {
 	__u8 reserved2[0x8];
 	/* WARNING: only valid for the first result due to variable sizes of
 	 *	    results */
-	struct hv_24x7_result results[1]; /* [@num_results] */
+	struct hv_24x7_result results[]; /* [@num_results] */
 } __packed;
 
 #endif
diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index 913c54e23eea..3a6dfd14f64b 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -124,7 +124,7 @@ config HV_PERF_CTRS
 	  Enable access to hypervisor supplied counters in perf. Currently,
 	  this enables code that uses the hcall GetPerfCounterInfo and 24x7
 	  interfaces to retrieve counters. GPCI exists on Power 6 and later
-	  systems. 24x7 is available on Power 8 systems.
+	  systems. 24x7 is available on Power 8 and later systems.
 
           If unsure, select Y.
 
-- 
2.7.4