From 9fb6c9b3fea1b1d1c6f14178373e8f7235f3b681 Mon Sep 17 00:00:00 2001
From: QingFeng Hao <haoqf@linux.vnet.ibm.com>
Date: Fri, 29 Sep 2017 12:41:51 +0200
Subject: s390/sthyi: add cache to store hypervisor info

STHYI requires extensive locking in the higher hypervisors and is
very computational/memory expensive. Therefore we cache the retrieved
hypervisor info whose valid period is 1s with mutex to allow concurrent
access. rw semaphore can't benefit here due to cache line bounce.

Signed-off-by: QingFeng Hao <haoqf@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/kernel/sthyi.c | 84 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 71 insertions(+), 13 deletions(-)

(limited to 'arch/s390/kernel')

diff --git a/arch/s390/kernel/sthyi.c b/arch/s390/kernel/sthyi.c
index 3d51f86f9dec..27e3c3d87379 100644
--- a/arch/s390/kernel/sthyi.c
+++ b/arch/s390/kernel/sthyi.c
@@ -11,7 +11,6 @@
 #include <linux/errno.h>
 #include <linux/pagemap.h>
 #include <linux/vmalloc.h>
-#include <linux/ratelimit.h>
 
 #include <asm/asm-offsets.h>
 #include <asm/sclp.h>
@@ -139,6 +138,21 @@ struct lpar_cpu_inf {
 	struct cpu_inf ifl;
 };
 
+/*
+ * STHYI requires extensive locking in the higher hypervisors
+ * and is very computational/memory expensive. Therefore we
+ * cache the retrieved data whose valid period is 1s.
+ */
+#define CACHE_VALID_JIFFIES	HZ
+
+struct sthyi_info {
+	void *info;
+	unsigned long end;
+};
+
+static DEFINE_MUTEX(sthyi_mutex);
+static struct sthyi_info sthyi_cache;
+
 static inline u64 cpu_id(u8 ctidx, void *diag224_buf)
 {
 	return *((u64 *)(diag224_buf + (ctidx + 1) * DIAG204_CPU_NAME_LEN));
@@ -395,6 +409,47 @@ static int sthyi(u64 vaddr, u64 *rc)
 	return cc;
 }
 
+static int fill_dst(void *dst, u64 *rc)
+{
+	struct sthyi_sctns *sctns = (struct sthyi_sctns *)dst;
+
+	/*
+	 * If the facility is on, we don't want to emulate the instruction.
+	 * We ask the hypervisor to provide the data.
+	 */
+	if (test_facility(74))
+		return sthyi((u64)dst, rc);
+
+	fill_hdr(sctns);
+	fill_stsi(sctns);
+	fill_diag(sctns);
+	*rc = 0;
+	return 0;
+}
+
+static int sthyi_init_cache(void)
+{
+	if (sthyi_cache.info)
+		return 0;
+	sthyi_cache.info = (void *)get_zeroed_page(GFP_KERNEL);
+	if (!sthyi_cache.info)
+		return -ENOMEM;
+	sthyi_cache.end = jiffies - 1; /* expired */
+	return 0;
+}
+
+static int sthyi_update_cache(u64 *rc)
+{
+	int r;
+
+	memset(sthyi_cache.info, 0, PAGE_SIZE);
+	r = fill_dst(sthyi_cache.info, rc);
+	if (r)
+		return r;
+	sthyi_cache.end = jiffies + CACHE_VALID_JIFFIES;
+	return r;
+}
+
 /*
  * sthyi_fill - Fill page with data returned by the STHYI instruction
  *
@@ -409,20 +464,23 @@ static int sthyi(u64 vaddr, u64 *rc)
  */
 int sthyi_fill(void *dst, u64 *rc)
 {
-	struct sthyi_sctns *sctns = (struct sthyi_sctns *)dst;
-
-	/*
-	 * If the facility is on, we don't want to emulate the instruction.
-	 * We ask the hypervisor to provide the data.
-	 */
-	if (test_facility(74))
-		return sthyi((u64)dst, rc);
+	int r;
 
-	fill_hdr(sctns);
-	fill_stsi(sctns);
-	fill_diag(sctns);
+	mutex_lock(&sthyi_mutex);
+	r = sthyi_init_cache();
+	if (r)
+		goto out;
 
+	if (time_is_before_jiffies(sthyi_cache.end)) {
+		/* cache expired */
+		r = sthyi_update_cache(rc);
+		if (r)
+			goto out;
+	}
 	*rc = 0;
-	return 0;
+	memcpy(dst, sthyi_cache.info, PAGE_SIZE);
+out:
+	mutex_unlock(&sthyi_mutex);
+	return r;
 }
 EXPORT_SYMBOL_GPL(sthyi_fill);
-- 
cgit