Re: powerpc/perf/hv-gpci: Increase request buffer size

quoted

From 31edd352fb7c2a72913f1977fa1bf168109089ad Mon Sep 17 00:00:00 2001

From: Sukadev Bhattiprolu <redacted>
Date: Tue, 9 Feb 2016 02:47:45 -0500
Subject: [PATCH] powerpc/perf/hv-gpci: Increase request buffer size

The GPCI hcall allows for a 4K buffer but we limit the buffer
to 1K. The problem with a 1K buffer is if a request results in
returning more values than can be accomodated in the 1K buffer
the request will fail.

The buffer we are using is currently allocated on the stack and
hence limited in size. Instead use a per-CPU 4K buffer like we do
with 24x7 counters (hv-24x7.c).

diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 856fe6e..e6fad73 100644
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c

@@ -127,8 +127,16 @@ static const struct attribute_group *attr_groups[] = {
 	NULL,
 };
 
+#define HGPCI_REQ_BUFFER_SIZE	4096
 #define GPCI_MAX_DATA_BYTES \
-	(1024 - sizeof(struct hv_get_perf_counter_info_params))
+	(HGPCI_REQ_BUFFER_SIZE - sizeof(struct hv_get_perf_counter_info_params))
+
+DEFINE_PER_CPU(char, hv_gpci_reqb[HGPCI_REQ_BUFFER_SIZE]) __aligned(sizeof(uint64_t));
+
+struct hv_gpci_request_buffer {
+	struct hv_get_perf_counter_info_params params;
+	uint8_t bytes[1];

@@ -163,9 +168,11 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
 	 */
 	count = 0;
 	for (i = offset; i < offset + length; i++)
-		count |= arg.bytes[i] << (i - offset);
+		count |= arg->bytes[i] << (i - offset);