Re: [PATCH v3 1/3] perf: Allow using AUX data in perf samples
From: Leo Yan
Date: Mon Nov 04 2019 - 07:30:16 EST
Hi Peter,
On Mon, Nov 04, 2019 at 11:16:58AM +0100, Peter Zijlstra wrote:
>
> Leo Yan,
>
> Since you were helpful in the other CS thread, could you please have a
> look to see if this interface will work for you guys?
Thanks a lot for reminding.
After a quick look, this patch set would be very useful; especially,
given Arm/Arm64 don't have LBR, this patch will be very helpful for
'virtual' branch recording on Arm/Arm64.
@Mathieu, could you review this patch set if you have bandwidth?
Since you implemented CoreSight snapshot mode so you have much deep
understanding than me :)
I will review and test this patch set in this week.
Thanks,
Leo Yan
P.s. one concern is how to allow this feature works with CS ETF/ETB;
ETF/ETB may be more suitable for 'virtual' branch recording due its
trace data is only several KiB but it's sufficient for 32 or 64
branch entries.
> On Fri, Oct 25, 2019 at 05:08:33PM +0300, Alexander Shishkin wrote:
> > AUX data can be used to annotate perf events such as performance counters
> > or tracepoints/breakpoints by including it in sample records when
> > PERF_SAMPLE_AUX flag is set. Such samples would be instrumental in debugging
> > and profiling by providing, for example, a history of instruction flow
> > leading up to the event's overflow.
> >
> > The implementation makes use of grouping an AUX event with all the events
> > that wish to take samples of the AUX data, such that the former is the
> > group leader. The samplees should also specify the desired size of the AUX
> > sample via attr.aux_sample_size.
> >
> > AUX capable PMUs need to explicitly add support for sampling, because it
> > relies on a new callback to take a snapshot of the buffer without touching
> > the event states.
> >
> > Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> > ---
> > include/linux/perf_event.h | 19 ++++
> > include/uapi/linux/perf_event.h | 10 +-
> > kernel/events/core.c | 172 +++++++++++++++++++++++++++++++-
> > kernel/events/internal.h | 1 +
> > kernel/events/ring_buffer.c | 36 +++++++
> > 5 files changed, 233 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 587ae4d002f5..446ce0014e89 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -249,6 +249,8 @@ struct perf_event;
> > #define PERF_PMU_CAP_NO_EXCLUDE 0x80
> > #define PERF_PMU_CAP_AUX_OUTPUT 0x100
> >
> > +struct perf_output_handle;
> > +
> > /**
> > * struct pmu - generic performance monitoring unit
> > */
> > @@ -423,6 +425,19 @@ struct pmu {
> > */
> > void (*free_aux) (void *aux); /* optional */
> >
> > + /*
> > + * Take a snapshot of the AUX buffer without touching the event
> > + * state, so that preempting ->start()/->stop() callbacks does
> > + * not interfere with their logic. Called in PMI context.
> > + *
> > + * Returns the size of AUX data copied to the output handle.
> > + *
> > + * Optional.
> > + */
> > + long (*snapshot_aux) (struct perf_event *event,
> > + struct perf_output_handle *handle,
> > + unsigned long size);
> > +
> > /*
> > * Validate address range filters: make sure the HW supports the
> > * requested configuration and number of filters; return 0 if the
> > @@ -964,6 +979,7 @@ struct perf_sample_data {
> > u32 reserved;
> > } cpu_entry;
> > struct perf_callchain_entry *callchain;
> > + u64 aux_size;
> >
> > /*
> > * regs_user may point to task_pt_regs or to regs_user_copy, depending
> > @@ -1353,6 +1369,9 @@ extern unsigned int perf_output_copy(struct perf_output_handle *handle,
> > const void *buf, unsigned int len);
> > extern unsigned int perf_output_skip(struct perf_output_handle *handle,
> > unsigned int len);
> > +extern long perf_output_copy_aux(struct perf_output_handle *aux_handle,
> > + struct perf_output_handle *handle,
> > + unsigned long from, unsigned long to);
> > extern int perf_swevent_get_recursion_context(void);
> > extern void perf_swevent_put_recursion_context(int rctx);
> > extern u64 perf_swevent_set_period(struct perf_event *event);
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index bb7b271397a6..377d794d3105 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -141,8 +141,9 @@ enum perf_event_sample_format {
> > PERF_SAMPLE_TRANSACTION = 1U << 17,
> > PERF_SAMPLE_REGS_INTR = 1U << 18,
> > PERF_SAMPLE_PHYS_ADDR = 1U << 19,
> > + PERF_SAMPLE_AUX = 1U << 20,
> >
> > - PERF_SAMPLE_MAX = 1U << 20, /* non-ABI */
> > + PERF_SAMPLE_MAX = 1U << 21, /* non-ABI */
> >
> > __PERF_SAMPLE_CALLCHAIN_EARLY = 1ULL << 63, /* non-ABI; internal use */
> > };
> > @@ -300,6 +301,7 @@ enum perf_event_read_format {
> > /* add: sample_stack_user */
> > #define PERF_ATTR_SIZE_VER4 104 /* add: sample_regs_intr */
> > #define PERF_ATTR_SIZE_VER5 112 /* add: aux_watermark */
> > +#define PERF_ATTR_SIZE_VER6 120 /* add: aux_sample_size */
> >
> > /*
> > * Hardware event_id to monitor via a performance monitoring event:
> > @@ -424,7 +426,9 @@ struct perf_event_attr {
> > */
> > __u32 aux_watermark;
> > __u16 sample_max_stack;
> > - __u16 __reserved_2; /* align to __u64 */
> > + __u16 __reserved_2;
> > + __u32 aux_sample_size;
> > + __u32 __reserved_3;
> > };
> >
> > /*
> > @@ -864,6 +868,8 @@ enum perf_event_type {
> > * { u64 abi; # enum perf_sample_regs_abi
> > * u64 regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
> > * { u64 phys_addr;} && PERF_SAMPLE_PHYS_ADDR
> > + * { u64 size;
> > + * char data[size]; } && PERF_SAMPLE_AUX
> > * };
> > */
> > PERF_RECORD_SAMPLE = 9,
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 0940c8810be0..36c612dbfcb0 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -1941,6 +1941,11 @@ static void perf_put_aux_event(struct perf_event *event)
> > }
> > }
> >
> > +static bool perf_need_aux_event(struct perf_event *event)
> > +{
> > + return !!event->attr.aux_output || !!event->attr.aux_sample_size;
> > +}
> > +
> > static int perf_get_aux_event(struct perf_event *event,
> > struct perf_event *group_leader)
> > {
> > @@ -1953,7 +1958,17 @@ static int perf_get_aux_event(struct perf_event *event,
> > if (!group_leader)
> > return 0;
> >
> > - if (!perf_aux_output_match(event, group_leader))
> > + /*
> > + * aux_output and aux_sample_size are mutually exclusive.
> > + */
> > + if (event->attr.aux_output && event->attr.aux_sample_size)
> > + return 0;
> > +
> > + if (event->attr.aux_output &&
> > + !perf_aux_output_match(event, group_leader))
> > + return 0;
> > +
> > + if (event->attr.aux_sample_size && !group_leader->pmu->snapshot_aux)
> > return 0;
> >
> > if (!atomic_long_inc_not_zero(&group_leader->refcount))
> > @@ -6192,6 +6207,121 @@ perf_output_sample_ustack(struct perf_output_handle *handle, u64 dump_size,
> > }
> > }
> >
> > +static unsigned long perf_aux_sample_size(struct perf_event *event,
> > + struct perf_sample_data *data,
> > + size_t size)
> > +{
> > + struct perf_event *sampler = event->aux_event;
> > + struct ring_buffer *rb;
> > +
> > + data->aux_size = 0;
> > +
> > + if (!sampler)
> > + goto out;
> > +
> > + if (WARN_ON_ONCE(READ_ONCE(sampler->state) != PERF_EVENT_STATE_ACTIVE))
> > + goto out;
> > +
> > + if (WARN_ON_ONCE(READ_ONCE(sampler->oncpu) != smp_processor_id()))
> > + goto out;
> > +
> > + rb = ring_buffer_get(sampler->parent ? sampler->parent : sampler);
> > + if (!rb)
> > + goto out;
> > +
> > + /*
> > + * If this is an NMI hit inside sampling code, don't take
> > + * the sample. See also perf_aux_sample_output().
> > + */
> > + if (READ_ONCE(rb->aux_in_sampling)) {
> > + data->aux_size = 0;
> > + } else {
> > + size = min_t(size_t, size, perf_aux_size(rb));
> > + data->aux_size = ALIGN(size, sizeof(u64));
> > + }
> > + ring_buffer_put(rb);
> > +
> > +out:
> > + return data->aux_size;
> > +}
> > +
> > +long perf_pmu_aux_sample_output(struct perf_event *event,
> > + struct perf_output_handle *handle,
> > + unsigned long size)
> > +{
> > + unsigned long flags;
> > + long ret;
> > +
> > + /*
> > + * Normal ->start()/->stop() callbacks run in IRQ mode in scheduler
> > + * paths. If we start calling them in NMI context, they may race with
> > + * the IRQ ones, that is, for example, re-starting an event that's just
> > + * been stopped, which is why we're using a separate callback that
> > + * doesn't change the event state.
> > + *
> > + * IRQs need to be disabled to prevent IPIs from racing with us.
> > + */
> > + local_irq_save(flags);
> > +
> > + ret = event->pmu->snapshot_aux(event, handle, size);
> > +
> > + local_irq_restore(flags);
> > +
> > + return ret;
> > +}
> > +
> > +static void perf_aux_sample_output(struct perf_event *event,
> > + struct perf_output_handle *handle,
> > + struct perf_sample_data *data)
> > +{
> > + struct perf_event *sampler = event->aux_event;
> > + unsigned long pad;
> > + struct ring_buffer *rb;
> > + long size;
> > +
> > + if (WARN_ON_ONCE(!sampler || !data->aux_size))
> > + return;
> > +
> > + rb = ring_buffer_get(sampler->parent ? sampler->parent : sampler);
> > + if (!rb)
> > + return;
> > +
> > + /*
> > + * Guard against NMI hits inside the critical section;
> > + * see also perf_aux_sample_size().
> > + */
> > + WRITE_ONCE(rb->aux_in_sampling, 1);
> > +
> > + size = perf_pmu_aux_sample_output(sampler, handle, data->aux_size);
> > +
> > + /*
> > + * An error here means that perf_output_copy() failed (returned a
> > + * non-zero surplus that it didn't copy), which in its current
> > + * enlightened implementation is not possible. If that changes, we'd
> > + * like to know.
> > + */
> > + if (WARN_ON_ONCE(size < 0))
> > + goto out_clear;
> > +
> > + /*
> > + * The pad comes from ALIGN()ing data->aux_size up to u64 in
> > + * perf_aux_sample_size(), so should not be more than that.
> > + */
> > + pad = data->aux_size - size;
> > + if (WARN_ON_ONCE(pad >= sizeof(u64)))
> > + pad = 8;
> > +
> > + if (pad) {
> > + u64 zero = 0;
> > + perf_output_copy(handle, &zero, pad);
> > + }
> > +
> > +out_clear:
> > + WRITE_ONCE(rb->aux_in_sampling, 0);
> > +
> > + ring_buffer_put(rb);
> > +}
> > +
> > static void __perf_event_header__init_id(struct perf_event_header *header,
> > struct perf_sample_data *data,
> > struct perf_event *event)
> > @@ -6511,6 +6641,13 @@ void perf_output_sample(struct perf_output_handle *handle,
> > if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> > perf_output_put(handle, data->phys_addr);
> >
> > + if (sample_type & PERF_SAMPLE_AUX) {
> > + perf_output_put(handle, data->aux_size);
> > +
> > + if (data->aux_size)
> > + perf_aux_sample_output(event, handle, data);
> > + }
> > +
> > if (!event->attr.watermark) {
> > int wakeup_events = event->attr.wakeup_events;
> >
> > @@ -6699,6 +6836,35 @@ void perf_prepare_sample(struct perf_event_header *header,
> >
> > if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> > data->phys_addr = perf_virt_to_phys(data->addr);
> > +
> > + if (sample_type & PERF_SAMPLE_AUX) {
> > + u64 size;
> > +
> > + header->size += sizeof(u64); /* size */
> > +
> > + /*
> > + * Given the 16bit nature of header::size, an AUX sample can
> > + * easily overflow it, what with all the preceding sample bits.
> > + * Make sure this doesn't happen by using up to U16_MAX bytes
> > + * per sample in total (rounded down to 8 byte boundary).
> > + */
> > + size = min_t(size_t, U16_MAX - header->size,
> > + event->attr.aux_sample_size);
> > + size = rounddown(size, 8);
> > + size = perf_aux_sample_size(event, data, size);
> > +
> > + WARN_ON_ONCE(size + header->size > U16_MAX);
> > + header->size += size;
> > + }
> > + /*
> > + * If you're adding more sample types here, you likely need to do
> > + * something about the overflowing header::size, like repurpose the
> > + * lowest 3 bits of size, which should be always zero at the moment.
> > + * This raises a more important question, do we really need 512k sized
> > + * samples and why, so good argumentation is in order for whatever you
> > + * do here next.
> > + */
> > + WARN_ON_ONCE(header->size & 7);
> > }
> >
> > static __always_inline int
> > @@ -10660,7 +10826,7 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
> >
> > attr->size = size;
> >
> > - if (attr->__reserved_1 || attr->__reserved_2)
> > + if (attr->__reserved_1 || attr->__reserved_2 || attr->__reserved_3)
> > return -EINVAL;
> >
> > if (attr->sample_type & ~(PERF_SAMPLE_MAX-1))
> > @@ -11210,7 +11376,7 @@ SYSCALL_DEFINE5(perf_event_open,
> > }
> > }
> >
> > - if (event->attr.aux_output && !perf_get_aux_event(event, group_leader))
> > + if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader))
> > goto err_locked;
> >
> > /*
> > diff --git a/kernel/events/internal.h b/kernel/events/internal.h
> > index 3aef4191798c..747d67f130cb 100644
> > --- a/kernel/events/internal.h
> > +++ b/kernel/events/internal.h
> > @@ -50,6 +50,7 @@ struct ring_buffer {
> > unsigned long aux_mmap_locked;
> > void (*free_aux)(void *);
> > refcount_t aux_refcount;
> > + int aux_in_sampling;
> > void **aux_pages;
> > void *aux_priv;
> >
> > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> > index 246c83ac5643..7ffd5c763f93 100644
> > --- a/kernel/events/ring_buffer.c
> > +++ b/kernel/events/ring_buffer.c
> > @@ -562,6 +562,42 @@ void *perf_get_aux(struct perf_output_handle *handle)
> > }
> > EXPORT_SYMBOL_GPL(perf_get_aux);
> >
> > +/*
> > + * Copy out AUX data from an AUX handle.
> > + */
> > +long perf_output_copy_aux(struct perf_output_handle *aux_handle,
> > + struct perf_output_handle *handle,
> > + unsigned long from, unsigned long to)
> > +{
> > + unsigned long tocopy, remainder, len = 0;
> > + struct ring_buffer *rb = aux_handle->rb;
> > + void *addr;
> > +
> > + from &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
> > + to &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
> > +
> > + do {
> > + tocopy = PAGE_SIZE - offset_in_page(from);
> > + if (to > from)
> > + tocopy = min(tocopy, to - from);
> > + if (!tocopy)
> > + break;
> > +
> > + addr = rb->aux_pages[from >> PAGE_SHIFT];
> > + addr += offset_in_page(from);
> > +
> > + remainder = perf_output_copy(handle, addr, tocopy);
> > + if (remainder)
> > + return -EFAULT;
> > +
> > + len += tocopy;
> > + from += tocopy;
> > + from &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
> > + } while (to != from);
> > +
> > + return len;
> > +}
> > +
> > #define PERF_AUX_GFP (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)
> >
> > static struct page *rb_alloc_aux_page(int node, int order)
> > --
> > 2.23.0
> >