linux-kernel - [PATCH v0 5/6] perf/x86/intel/pt: Free up space in a ToPA descriptor

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Message-Id: <20190821124727.73310-6-alexander.shishkin@linux.intel.com>
Date:   Wed, 21 Aug 2019 15:47:26 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: [PATCH v0 5/6] perf/x86/intel/pt: Free up space in a ToPA descriptor

Currently, we're storing physical address of a ToPA table in its
descriptor, which is completely unnecessary. Since the descriptor
and the table itself share the same page, reducing the descriptor
size leaves more space for the table.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 arch/x86/events/intel/pt.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index e7b0f8f4f1b0..5965e9493c8b 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -548,14 +548,12 @@ static void pt_config_buffer(void *buf, unsigned int topa_idx,
 /**
  * struct topa - ToPA metadata
  * @list:	linkage to struct pt_buffer's list of tables
- * @phys:	physical address of this page
  * @offset:	offset of the first entry in this table in the buffer
  * @size:	total size of all entries in this table
  * @last:	index of the last initialized entry in this table
  */
 struct topa {
 	struct list_head	list;
-	u64			phys;
 	u64			offset;
 	size_t			size;
 	int			last;
@@ -589,6 +587,11 @@ static inline struct topa_page *topa_entry_to_page(struct topa_entry *te)
 	return (struct topa_page *)((unsigned long)te & PAGE_MASK);
 }
 
+static inline phys_addr_t topa_pfn(struct topa *topa)
+{
+	return PFN_DOWN(virt_to_phys(topa_to_page(topa)));
+}
+
 /* make -1 stand for the last table entry */
 #define TOPA_ENTRY(t, i)				\
 	((i) == -1					\
@@ -615,14 +618,13 @@ static struct topa *topa_alloc(int cpu, gfp_t gfp)
 
 	tp = page_address(p);
 	tp->topa.last = 0;
-	tp->topa.phys = page_to_phys(p);
 
 	/*
 	 * In case of singe-entry ToPA, always put the self-referencing END
 	 * link as the 2nd entry in the table
 	 */
 	if (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries)) {
-		TOPA_ENTRY(&tp->topa, 1)->base = tp->topa.phys;
+		TOPA_ENTRY(&tp->topa, 1)->base = page_to_phys(p);
 		TOPA_ENTRY(&tp->topa, 1)->end = 1;
 	}
 
@@ -666,7 +668,7 @@ static void topa_insert_table(struct pt_buffer *buf, struct topa *topa)
 
 	BUG_ON(last->last != TENTS_PER_PAGE - 1);
 
-	TOPA_ENTRY(last, -1)->base = topa->phys >> TOPA_SHIFT;
+	TOPA_ENTRY(last, -1)->base = topa_pfn(topa);
 	TOPA_ENTRY(last, -1)->end = 1;
 }
 
@@ -739,8 +741,8 @@ static void pt_topa_dump(struct pt_buffer *buf)
 		struct topa_page *tp = topa_to_page(topa);
 		int i;
 
-		pr_debug("# table @%p (%016Lx), off %llx size %zx\n", tp->table,
-			 topa->phys, topa->offset, topa->size);
+		pr_debug("# table @%p, off %llx size %zx\n", tp->table,
+			 topa->offset, topa->size);
 		for (i = 0; i < TENTS_PER_PAGE; i++) {
 			pr_debug("# entry @%p (%lx sz %u %c%c%c) raw=%16llx\n",
 				 &tp->table[i],
@@ -1111,7 +1113,7 @@ static int pt_buffer_init_topa(struct pt_buffer *buf, int cpu,
 
 	/* link last table to the first one, unless we're double buffering */
 	if (intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries)) {
-		TOPA_ENTRY(buf->last, -1)->base = buf->first->phys >> TOPA_SHIFT;
+		TOPA_ENTRY(buf->last, -1)->base = topa_pfn(buf->first);
 		TOPA_ENTRY(buf->last, -1)->end = 1;
 	}
 
-- 
2.23.0.rc1