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Date: Wed, 21 May 2014 17:02:10 +0300
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
Frederic Weisbecker <fweisbec@...il.com>,
Mike Galbraith <efault@....de>,
Paul Mackerras <paulus@...ba.org>,
Stephane Eranian <eranian@...gle.com>,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC 2/2] perf: add AUX area to ring buffer for raw data streams
Peter Zijlstra <peterz@...radead.org> writes:
> On Mon, May 19, 2014 at 03:57:37PM +0300, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@...radead.org> writes:
>
>> > I'm not entirely thrilled to expose it to the PMU like this.. I realize
>> > you want this in order to get physically contiguous pages.
>>
>> Hmm, I guess we can have code in perf core to carry out the allocation
>> according to, say, contstraint flags and pass the page array down to the
>> PMU if that sounds like a cleaner thing to do?
>>
>> > Are you aware of allocation constraints for other architectures?
>>
>> Somewhat. ARM's trace memory controller supports both scatter-gather and
>> a plain contiguous buffer, I haven't found evidence of one being
>> available while the other one isn't, so I'm inclined to assume that if
>> it can write to system memory, it supports SG.
>
> I've just added a patch from Vince Weaver:
>
> http://lkml.kernel.org/r/alpine.DEB.2.10.1405161708060.11099@vincent-weaver-1.umelst.maine.edu
>
> That adds pmu::capabilities, I suppose we could start with something
> like:
>
> PERF_PMU_CAP_AUX_BROKEN_SG
>
> which would make the allocator attempt to fill the AUX buffer with as
> big a chunks of contiguous memory as is available.
Ok, how about this (on top of the previous patch):
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9643450..e2a6b6b 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -278,15 +278,15 @@ struct pmu {
void (*flush_branch_stack) (void);
/*
- * Allocate AUX space buffer: return an array of @nr_pages pages to be
- * mapped to userspace that will also be passed to ->free_aux.
+ * Set up pmu-private data structures for an AUX area
*/
- void *(*alloc_aux) (int cpu, int nr_pages, bool overwrite,
+ void *(*setup_aux) (int cpu, void **pages,
+ int nr_pages, bool overwrite,
struct perf_event_mmap_page *user_page);
/* optional */
/*
- * Free AUX buffer
+ * Free pmu-private AUX data structures
*/
void (*free_aux) (void *aux); /* optional */
@@ -300,6 +300,7 @@ struct pmu {
* struct pmu::capabilities flags
*/
#define PERF_PMU_CAP_NO_INTERRUPT 1
+#define PERF_PMU_CAP_AUX_BROKEN_SG 2
/**
* enum perf_event_active_state - the states of a event
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index ea51cfb..a06d7fe 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -41,6 +41,7 @@ struct ring_buffer {
atomic_t aux_mmap_count;
unsigned long aux_mmap_locked;
void **aux_pages;
+ void *aux_priv;
void (*free_aux)(void *aux);
struct perf_event_mmap_page *user_page;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 5935cb2..7f166f2 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -244,32 +244,96 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
spin_lock_init(&rb->event_lock);
}
+#define PERF_AUX_GFP (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)
+
+static struct page *rb_alloc_aux_page(int node, int order)
+{
+ struct page *page;
+
+ if (order > MAX_ORDER)
+ order = MAX_ORDER;
+
+ do {
+ page = alloc_pages_node(node, PERF_AUX_GFP, order);
+ } while (!page && order--);
+
+ if (page && order) {
+ /*
+ * Communicate the allocation size to the driver
+ */
+ split_page(page, order);
+ SetPagePrivate(page);
+ set_page_private(page, order);
+ }
+
+ return page;
+}
+
+static void rb_free_aux_page(struct ring_buffer *rb, int idx)
+{
+ struct page *page = virt_to_page(rb->aux_pages[idx]);
+
+ ClearPagePrivate(page);
+ page->mapping = NULL;
+ __free_page(page);
+}
+
int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
pgoff_t pgoff, int nr_pages, int flags)
{
bool overwrite = !!(flags & RING_BUFFER_WRITABLE);
+ int pg, node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
+ int order = 0;
- if (!event->pmu->alloc_aux)
+ if (!event->pmu->setup_aux)
return -ENOTSUPP;
- rb->aux_pages = event->pmu->alloc_aux(event->cpu, nr_pages, overwrite,
- rb->user_page);
+ if (event->pmu->capabilities & PERF_PMU_CAP_AUX_BROKEN_SG)
+ order = get_order(nr_pages * PAGE_SIZE);
+
+ rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
if (!rb->aux_pages)
return -ENOMEM;
+ for (pg = 0; pg < nr_pages;) {
+ struct page *page;
+ int last;
+
+ page = rb_alloc_aux_page(node, order);
+ if (!page)
+ goto err;
+
+ for (last = pg + (1 << page_private(page)); pg < last; pg++)
+ rb->aux_pages[pg] = page_address(page++);
+ }
+
+ rb->aux_priv = event->pmu->setup_aux(event->cpu, rb->aux_pages, nr_pages,
+ overwrite, rb->user_page);
+ if (!rb->aux_priv) {
+ rb_free_aux(rb);
+ return -EINVAL;
+ }
+
rb->free_aux = event->pmu->free_aux;
rb->aux_pgoff = pgoff;
rb->aux_nr_pages = nr_pages;
return 0;
+err:
+ for (; pg >= 0; pg--)
+ rb_free_aux_page(rb, pg);
+
+ return -ENOMEM;
}
void rb_free_aux(struct ring_buffer *rb)
{
- if (WARN_ON_ONCE(!rb->free_aux))
- return;
+ int pg;
+
+ for (pg = 0; pg < rb->aux_nr_pages; pg++)
+ rb_free_aux_page(rb, pg);
- rb->free_aux(rb->aux_pages);
+ rb->free_aux(rb->aux_priv);
rb->aux_nr_pages = 0;
}
>> > That appears to be missing a is_power_of_2(aux_size) check.
>> >
>> > The problem with not having that is that since
>> > perf_event_mmap_page::aux_{head,tail} are of Z mod 2^64 but your actual
>> > {head,tail} are of Z mod aux_size, you need aux_size to be a full
>> > divider of 2^64 or otherwise you get wrapping issues at the overflow.
>> >
>> > Having it them all 2^n makes the divider trivial.
>>
>> I left it out so that the PMU callback could decide if it wants to do
>> the math or not. Maybe it can also be a constraint flag or is it not
>> worth it at all?
>
> I'd start with the most constrained model -- that is add the power of
> two test -- and worry about relaxing it if it turns out its really
> needed.
Makes sense, I'll put it back.
Regards,
--
Alex
--
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