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From: Peter Zijlstra on 21 May 2010 05:20
Sanity checks cost instructions

Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
---
include/linux/perf_event.h | 2 --
kernel/perf_event.c | 20 ++++----------------
2 files changed, 4 insertions(+), 18 deletions(-)

Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h
+++ linux-2.6/include/linux/perf_event.h
@@ -803,8 +803,6 @@ struct perf_cpu_context {
struct perf_output_handle {
struct perf_event *event;
struct perf_mmap_data *data;
- unsigned long head;
- unsigned long offset;
unsigned long wakeup;
unsigned long size;
void *addr;
Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -2966,20 +2966,11 @@ again:
preempt_enable();
}

-void perf_output_copy(struct perf_output_handle *handle,
+__always_inline void perf_output_copy(struct perf_output_handle *handle,
const void *buf, unsigned int len)
{
- handle->offset += len;
-
- /*
- * Check we didn't copy past our reservation window, taking the
- * possible unsigned int wrap into account.
- */
- if (WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0))
- return;
-
do {
- unsigned long size = min(handle->size, len);
+ unsigned long size = min_t(unsigned long, handle->size, len);

memcpy(handle->addr, buf, size);

@@ -3054,15 +3045,12 @@ int perf_output_begin(struct perf_output
goto fail;
} while (local_cmpxchg(&data->head, offset, head) != offset);

- handle->offset = offset;
- handle->head = head;
-
if (head - local_read(&data->wakeup) > data->watermark)
local_add(data->watermark, &data->wakeup);

- handle->page = handle->offset >> (PAGE_SHIFT + page_order(data));
+ handle->page = offset >> (PAGE_SHIFT + page_order(data));
handle->page &= data->nr_pages - 1;
- handle->size = handle->offset & ((PAGE_SIZE << page_order(data)) - 1);
+ handle->size = offset & ((PAGE_SIZE << page_order(data)) - 1);
handle->addr = data->data_pages[handle->page];
handle->addr += handle->size;
handle->size = (PAGE_SIZE << page_order(data)) - handle->size;


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Prev: [PATCH] [WATCHDOG] bfin: use new common Blackfin watchdog header
Next: [PATCH 06/10] perf: Fix wakeup storm for RO mmap()s