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authorLinus Torvalds <torvalds@linux-foundation.org>2009-10-08 12:05:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-10-08 12:05:50 -0700
commitb924f9599dfd4a604761e84b1e920e480fb57f66 (patch)
treea1456ef8aea8beb8415d8258a978e072467d8ff6
parentb9d40b7b1e349bdc5c174b4ef1a333e62f7d749c (diff)
parent2dca6999eed58d44b67e9de7d6ec230f6250553d (diff)
downloadlinux-linaro-b924f9599dfd4a604761e84b1e920e480fb57f66.tar.gz
Merge branch 'sparc-perf-events-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sparc-perf-events-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: mm, perf_event: Make vmalloc_user() align base kernel virtual address to SHMLBA perf_event: Provide vmalloc() based mmap() backing
-rw-r--r--arch/sparc/Kconfig2
-rw-r--r--include/linux/perf_event.h5
-rw-r--r--init/Kconfig18
-rw-r--r--kernel/perf_event.c248
-rw-r--r--mm/vmalloc.c48
-rw-r--r--tools/perf/design.txt3
6 files changed, 240 insertions, 84 deletions
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index ac45aab741a..05ef5380a68 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -26,6 +26,7 @@ config SPARC
select RTC_CLASS
select RTC_DRV_M48T59
select HAVE_PERF_EVENTS
+ select PERF_USE_VMALLOC
select HAVE_DMA_ATTRS
select HAVE_DMA_API_DEBUG
@@ -48,6 +49,7 @@ config SPARC64
select RTC_DRV_SUN4V
select RTC_DRV_STARFIRE
select HAVE_PERF_EVENTS
+ select PERF_USE_VMALLOC
config ARCH_DEFCONFIG
string
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3a9d36d1e92..2e6d95f9741 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -442,6 +442,7 @@ enum perf_callchain_context {
#include <linux/hrtimer.h>
#include <linux/fs.h>
#include <linux/pid_namespace.h>
+#include <linux/workqueue.h>
#include <asm/atomic.h>
#define PERF_MAX_STACK_DEPTH 255
@@ -513,6 +514,10 @@ struct file;
struct perf_mmap_data {
struct rcu_head rcu_head;
+#ifdef CONFIG_PERF_USE_VMALLOC
+ struct work_struct work;
+#endif
+ int data_order;
int nr_pages; /* nr of data pages */
int writable; /* are we writable */
int nr_locked; /* nr pages mlocked */
diff --git a/init/Kconfig b/init/Kconfig
index c7bac39d6c6..09c5c6431f4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -921,6 +921,11 @@ config HAVE_PERF_EVENTS
help
See tools/perf/design.txt for details.
+config PERF_USE_VMALLOC
+ bool
+ help
+ See tools/perf/design.txt for details
+
menu "Kernel Performance Events And Counters"
config PERF_EVENTS
@@ -976,6 +981,19 @@ config PERF_COUNTERS
Say N if unsure.
+config DEBUG_PERF_USE_VMALLOC
+ default n
+ bool "Debug: use vmalloc to back perf mmap() buffers"
+ depends on PERF_EVENTS && DEBUG_KERNEL
+ select PERF_USE_VMALLOC
+ help
+ Use vmalloc memory to back perf mmap() buffers.
+
+ Mostly useful for debugging the vmalloc code on platforms
+ that don't require it.
+
+ Say N if unsure.
+
endmenu
config VM_EVENT_COUNTERS
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index e491fb08793..9d0b5c66588 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -20,6 +20,7 @@
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/vmstat.h>
+#include <linux/vmalloc.h>
#include <linux/hardirq.h>
#include <linux/rculist.h>
#include <linux/uaccess.h>
@@ -2091,49 +2092,31 @@ unlock:
rcu_read_unlock();
}
-static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+static unsigned long perf_data_size(struct perf_mmap_data *data)
{
- struct perf_event *event = vma->vm_file->private_data;
- struct perf_mmap_data *data;
- int ret = VM_FAULT_SIGBUS;
-
- if (vmf->flags & FAULT_FLAG_MKWRITE) {
- if (vmf->pgoff == 0)
- ret = 0;
- return ret;
- }
-
- rcu_read_lock();
- data = rcu_dereference(event->data);
- if (!data)
- goto unlock;
-
- if (vmf->pgoff == 0) {
- vmf->page = virt_to_page(data->user_page);
- } else {
- int nr = vmf->pgoff - 1;
-
- if ((unsigned)nr > data->nr_pages)
- goto unlock;
+ return data->nr_pages << (PAGE_SHIFT + data->data_order);
+}
- if (vmf->flags & FAULT_FLAG_WRITE)
- goto unlock;
+#ifndef CONFIG_PERF_USE_VMALLOC
- vmf->page = virt_to_page(data->data_pages[nr]);
- }
+/*
+ * Back perf_mmap() with regular GFP_KERNEL-0 pages.
+ */
- get_page(vmf->page);
- vmf->page->mapping = vma->vm_file->f_mapping;
- vmf->page->index = vmf->pgoff;
+static struct page *
+perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
+{
+ if (pgoff > data->nr_pages)
+ return NULL;
- ret = 0;
-unlock:
- rcu_read_unlock();
+ if (pgoff == 0)
+ return virt_to_page(data->user_page);
- return ret;
+ return virt_to_page(data->data_pages[pgoff - 1]);
}
-static int perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
+static struct perf_mmap_data *
+perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
{
struct perf_mmap_data *data;
unsigned long size;
@@ -2158,19 +2141,10 @@ static int perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
goto fail_data_pages;
}
+ data->data_order = 0;
data->nr_pages = nr_pages;
- atomic_set(&data->lock, -1);
-
- if (event->attr.watermark) {
- data->watermark = min_t(long, PAGE_SIZE * nr_pages,
- event->attr.wakeup_watermark);
- }
- if (!data->watermark)
- data->watermark = max(PAGE_SIZE, PAGE_SIZE * nr_pages / 4);
- rcu_assign_pointer(event->data, data);
-
- return 0;
+ return data;
fail_data_pages:
for (i--; i >= 0; i--)
@@ -2182,7 +2156,7 @@ fail_user_page:
kfree(data);
fail:
- return -ENOMEM;
+ return NULL;
}
static void perf_mmap_free_page(unsigned long addr)
@@ -2193,28 +2167,169 @@ static void perf_mmap_free_page(unsigned long addr)
__free_page(page);
}
-static void __perf_mmap_data_free(struct rcu_head *rcu_head)
+static void perf_mmap_data_free(struct perf_mmap_data *data)
{
- struct perf_mmap_data *data;
int i;
- data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
-
perf_mmap_free_page((unsigned long)data->user_page);
for (i = 0; i < data->nr_pages; i++)
perf_mmap_free_page((unsigned long)data->data_pages[i]);
+}
+
+#else
+
+/*
+ * Back perf_mmap() with vmalloc memory.
+ *
+ * Required for architectures that have d-cache aliasing issues.
+ */
+
+static struct page *
+perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
+{
+ if (pgoff > (1UL << data->data_order))
+ return NULL;
+
+ return vmalloc_to_page((void *)data->user_page + pgoff * PAGE_SIZE);
+}
+
+static void perf_mmap_unmark_page(void *addr)
+{
+ struct page *page = vmalloc_to_page(addr);
+
+ page->mapping = NULL;
+}
+
+static void perf_mmap_data_free_work(struct work_struct *work)
+{
+ struct perf_mmap_data *data;
+ void *base;
+ int i, nr;
+
+ data = container_of(work, struct perf_mmap_data, work);
+ nr = 1 << data->data_order;
+
+ base = data->user_page;
+ for (i = 0; i < nr + 1; i++)
+ perf_mmap_unmark_page(base + (i * PAGE_SIZE));
+
+ vfree(base);
+}
+
+static void perf_mmap_data_free(struct perf_mmap_data *data)
+{
+ schedule_work(&data->work);
+}
+
+static struct perf_mmap_data *
+perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
+{
+ struct perf_mmap_data *data;
+ unsigned long size;
+ void *all_buf;
+ WARN_ON(atomic_read(&event->mmap_count));
+
+ size = sizeof(struct perf_mmap_data);
+ size += sizeof(void *);
+
+ data = kzalloc(size, GFP_KERNEL);
+ if (!data)
+ goto fail;
+
+ INIT_WORK(&data->work, perf_mmap_data_free_work);
+
+ all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
+ if (!all_buf)
+ goto fail_all_buf;
+
+ data->user_page = all_buf;
+ data->data_pages[0] = all_buf + PAGE_SIZE;
+ data->data_order = ilog2(nr_pages);
+ data->nr_pages = 1;
+
+ return data;
+
+fail_all_buf:
+ kfree(data);
+
+fail:
+ return NULL;
+}
+
+#endif
+
+static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+ struct perf_event *event = vma->vm_file->private_data;
+ struct perf_mmap_data *data;
+ int ret = VM_FAULT_SIGBUS;
+
+ if (vmf->flags & FAULT_FLAG_MKWRITE) {
+ if (vmf->pgoff == 0)
+ ret = 0;
+ return ret;
+ }
+
+ rcu_read_lock();
+ data = rcu_dereference(event->data);
+ if (!data)
+ goto unlock;
+
+ if (vmf->pgoff && (vmf->flags & FAULT_FLAG_WRITE))
+ goto unlock;
+
+ vmf->page = perf_mmap_to_page(data, vmf->pgoff);
+ if (!vmf->page)
+ goto unlock;
+
+ get_page(vmf->page);
+ vmf->page->mapping = vma->vm_file->f_mapping;
+ vmf->page->index = vmf->pgoff;
+
+ ret = 0;
+unlock:
+ rcu_read_unlock();
+
+ return ret;
+}
+
+static void
+perf_mmap_data_init(struct perf_event *event, struct perf_mmap_data *data)
+{
+ long max_size = perf_data_size(data);
+
+ atomic_set(&data->lock, -1);
+
+ if (event->attr.watermark) {
+ data->watermark = min_t(long, max_size,
+ event->attr.wakeup_watermark);
+ }
+
+ if (!data->watermark)
+ data->watermark = max_t(long, PAGE_SIZE, max_size / 2);
+
+
+ rcu_assign_pointer(event->data, data);
+}
+
+static void perf_mmap_data_free_rcu(struct rcu_head *rcu_head)
+{
+ struct perf_mmap_data *data;
+
+ data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
+ perf_mmap_data_free(data);
kfree(data);
}
-static void perf_mmap_data_free(struct perf_event *event)
+static void perf_mmap_data_release(struct perf_event *event)
{
struct perf_mmap_data *data = event->data;
WARN_ON(atomic_read(&event->mmap_count));
rcu_assign_pointer(event->data, NULL);
- call_rcu(&data->rcu_head, __perf_mmap_data_free);
+ call_rcu(&data->rcu_head, perf_mmap_data_free_rcu);
}
static void perf_mmap_open(struct vm_area_struct *vma)
@@ -2230,11 +2345,12 @@ static void perf_mmap_close(struct vm_area_struct *vma)
WARN_ON_ONCE(event->ctx->parent_ctx);
if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
+ unsigned long size = perf_data_size(event->data);
struct user_struct *user = current_user();
- atomic_long_sub(event->data->nr_pages + 1, &user->locked_vm);
+ atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm);
vma->vm_mm->locked_vm -= event->data->nr_locked;
- perf_mmap_data_free(event);
+ perf_mmap_data_release(event);
mutex_unlock(&event->mmap_mutex);
}
}
@@ -2252,6 +2368,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
unsigned long user_locked, user_lock_limit;
struct user_struct *user = current_user();
unsigned long locked, lock_limit;
+ struct perf_mmap_data *data;
unsigned long vma_size;
unsigned long nr_pages;
long user_extra, extra;
@@ -2314,10 +2431,15 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
}
WARN_ON(event->data);
- ret = perf_mmap_data_alloc(event, nr_pages);
- if (ret)
+
+ data = perf_mmap_data_alloc(event, nr_pages);
+ ret = -ENOMEM;
+ if (!data)
goto unlock;
+ ret = 0;
+ perf_mmap_data_init(event, data);
+
atomic_set(&event->mmap_count, 1);
atomic_long_add(user_extra, &user->locked_vm);
vma->vm_mm->locked_vm += extra;
@@ -2505,7 +2627,7 @@ static bool perf_output_space(struct perf_mmap_data *data, unsigned long tail,
if (!data->writable)
return true;
- mask = (data->nr_pages << PAGE_SHIFT) - 1;
+ mask = perf_data_size(data) - 1;
offset = (offset - tail) & mask;
head = (head - tail) & mask;
@@ -2610,7 +2732,7 @@ void perf_output_copy(struct perf_output_handle *handle,
const void *buf, unsigned int len)
{
unsigned int pages_mask;
- unsigned int offset;
+ unsigned long offset;
unsigned int size;
void **pages;
@@ -2619,12 +2741,14 @@ void perf_output_copy(struct perf_output_handle *handle,
pages = handle->data->data_pages;
do {
- unsigned int page_offset;
+ unsigned long page_offset;
+ unsigned long page_size;
int nr;
nr = (offset >> PAGE_SHIFT) & pages_mask;
- page_offset = offset & (PAGE_SIZE - 1);
- size = min_t(unsigned int, PAGE_SIZE - page_offset, len);
+ page_size = 1UL << (handle->data->data_order + PAGE_SHIFT);
+ page_offset = offset & (page_size - 1);
+ size = min_t(unsigned int, page_size - page_offset, len);
memcpy(pages[nr] + page_offset, buf, size);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 2f7c9d75c55..5e7aed0802b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -28,6 +28,7 @@
#include <asm/atomic.h>
#include <asm/uaccess.h>
#include <asm/tlbflush.h>
+#include <asm/shmparam.h>
/*** Page table manipulation functions ***/
@@ -1155,12 +1156,11 @@ static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
}
static struct vm_struct *__get_vm_area_node(unsigned long size,
- unsigned long flags, unsigned long start, unsigned long end,
- int node, gfp_t gfp_mask, void *caller)
+ unsigned long align, unsigned long flags, unsigned long start,
+ unsigned long end, int node, gfp_t gfp_mask, void *caller)
{
static struct vmap_area *va;
struct vm_struct *area;
- unsigned long align = 1;
BUG_ON(in_interrupt());
if (flags & VM_IOREMAP) {
@@ -1200,7 +1200,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
unsigned long start, unsigned long end)
{
- return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL,
+ return __get_vm_area_node(size, 1, flags, start, end, -1, GFP_KERNEL,
__builtin_return_address(0));
}
EXPORT_SYMBOL_GPL(__get_vm_area);
@@ -1209,7 +1209,7 @@ struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
unsigned long start, unsigned long end,
void *caller)
{
- return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL,
+ return __get_vm_area_node(size, 1, flags, start, end, -1, GFP_KERNEL,
caller);
}
@@ -1224,22 +1224,22 @@ struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
*/
struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
{
- return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END,
+ return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
-1, GFP_KERNEL, __builtin_return_address(0));
}
struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags,
void *caller)
{
- return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END,
+ return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
-1, GFP_KERNEL, caller);
}
struct vm_struct *get_vm_area_node(unsigned long size, unsigned long flags,
int node, gfp_t gfp_mask)
{
- return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END, node,
- gfp_mask, __builtin_return_address(0));
+ return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
+ node, gfp_mask, __builtin_return_address(0));
}
static struct vm_struct *find_vm_area(const void *addr)
@@ -1402,7 +1402,8 @@ void *vmap(struct page **pages, unsigned int count,
}
EXPORT_SYMBOL(vmap);
-static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
+static void *__vmalloc_node(unsigned long size, unsigned long align,
+ gfp_t gfp_mask, pgprot_t prot,
int node, void *caller);
static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
pgprot_t prot, int node, void *caller)
@@ -1416,7 +1417,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
area->nr_pages = nr_pages;
/* Please note that the recursion is strictly bounded. */
if (array_size > PAGE_SIZE) {
- pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
+ pages = __vmalloc_node(array_size, 1, gfp_mask | __GFP_ZERO,
PAGE_KERNEL, node, caller);
area->flags |= VM_VPAGES;
} else {
@@ -1475,6 +1476,7 @@ void *__vmalloc_area(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot)
/**
* __vmalloc_node - allocate virtually contiguous memory
* @size: allocation size
+ * @align: desired alignment
* @gfp_mask: flags for the page level allocator
* @prot: protection mask for the allocated pages
* @node: node to use for allocation or -1
@@ -1484,8 +1486,9 @@ void *__vmalloc_area(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot)
* allocator with @gfp_mask flags. Map them into contiguous
* kernel virtual space, using a pagetable protection of @prot.
*/
-static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
- int node, void *caller)
+static void *__vmalloc_node(unsigned long size, unsigned long align,
+ gfp_t gfp_mask, pgprot_t prot,
+ int node, void *caller)
{
struct vm_struct *area;
void *addr;
@@ -1495,8 +1498,8 @@ static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
if (!size || (size >> PAGE_SHIFT) > totalram_pages)
return NULL;
- area = __get_vm_area_node(size, VM_ALLOC, VMALLOC_START, VMALLOC_END,
- node, gfp_mask, caller);
+ area = __get_vm_area_node(size, align, VM_ALLOC, VMALLOC_START,
+ VMALLOC_END, node, gfp_mask, caller);
if (!area)
return NULL;
@@ -1515,7 +1518,7 @@ static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
{
- return __vmalloc_node(size, gfp_mask, prot, -1,
+ return __vmalloc_node(size, 1, gfp_mask, prot, -1,
__builtin_return_address(0));
}
EXPORT_SYMBOL(__vmalloc);
@@ -1531,7 +1534,7 @@ EXPORT_SYMBOL(__vmalloc);
*/
void *vmalloc(unsigned long size)
{
- return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
+ return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
-1, __builtin_return_address(0));
}
EXPORT_SYMBOL(vmalloc);
@@ -1548,7 +1551,8 @@ void *vmalloc_user(unsigned long size)
struct vm_struct *area;
void *ret;
- ret = __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
+ ret = __vmalloc_node(size, SHMLBA,
+ GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
PAGE_KERNEL, -1, __builtin_return_address(0));
if (ret) {
area = find_vm_area(ret);
@@ -1571,7 +1575,7 @@ EXPORT_SYMBOL(vmalloc_user);
*/
void *vmalloc_node(unsigned long size, int node)
{
- return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
+ return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
node, __builtin_return_address(0));
}
EXPORT_SYMBOL(vmalloc_node);
@@ -1594,7 +1598,7 @@ EXPORT_SYMBOL(vmalloc_node);
void *vmalloc_exec(unsigned long size)
{
- return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC,
+ return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC,
-1, __builtin_return_address(0));
}
@@ -1615,7 +1619,7 @@ void *vmalloc_exec(unsigned long size)
*/
void *vmalloc_32(unsigned long size)
{
- return __vmalloc_node(size, GFP_VMALLOC32, PAGE_KERNEL,
+ return __vmalloc_node(size, 1, GFP_VMALLOC32, PAGE_KERNEL,
-1, __builtin_return_address(0));
}
EXPORT_SYMBOL(vmalloc_32);
@@ -1632,7 +1636,7 @@ void *vmalloc_32_user(unsigned long size)
struct vm_struct *area;
void *ret;
- ret = __vmalloc_node(size, GFP_VMALLOC32 | __GFP_ZERO, PAGE_KERNEL,
+ ret = __vmalloc_node(size, 1, GFP_VMALLOC32 | __GFP_ZERO, PAGE_KERNEL,
-1, __builtin_return_address(0));
if (ret) {
area = find_vm_area(ret);
diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index f1946d107b1..fdd42a824c9 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt
@@ -455,3 +455,6 @@ will need at least this:
If your architecture does have hardware capabilities, you can override the
weak stub hw_perf_event_init() to register hardware counters.
+
+Architectures that have d-cache aliassing issues, such as Sparc and ARM,
+should select PERF_USE_VMALLOC in order to avoid these for perf mmap().