RE: [PATCH 1/8] perf: Add PERF_SAMPLE_PHYS_ADDR

From: Liang, Kan
Date: Fri Jan 08 2016 - 16:12:46 EST

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>
> On Wed, Jan 6, 2016 at 3:04 AM, <kan.liang@xxxxxxxxx> wrote:
> > From: Kan Liang <kan.liang@xxxxxxxxx>
> >
> > For understanding how the workload maps to memory channels and
> > hardware behavior, it's useful to collect address maps with physical
> addresses.
> > This is not intended for detecting page sharing (which can be already
> > done using the mmap inode), but for lower level hardware behavior
> > studies.
> > Perf supports load latency/DLA which can only collect virtual addresses.
> > This patch add a new sample type PERF_SAMPLE_PHYS_ADDR to expose
> the
> > physical addresses.
> > For kernel direct mapping addresses, the patch uses virt_to_phys to
> > convert the virtual addresses from DLA to physical address.
> > For user virtual addresses, __get_user_pages_fast is used to walk the
> > pages tables for user physical address.
> > This does not work for vmalloc addresses. Right now these are not
> > resolved, but code to do that could be added.
> > For security, the physical address can only be exposed to root or
> > privileged user.
> >
> The other limitation of your patch series is that it is providing physical
> address for data only. It does not cover code, i.e., it is not possible to
> obtain the physical address of a sampled IP. So maybe the new
> sample_type should be renamed to PERF_SAMPLE_DATA_PHYS_ADDR
> instead.

We use sample_type PERF_SAMPLE_ADDR for the data virtual address.
So in this patch I choose a similar name PERF_SAMPLE_PHYS_ADDR for
data physical address. I think it should not lead to ambiguity.

> Should you add physical addresses for IP (no need for PEBS for this), then
> you'd have to have a new name, anyway.

We use another sample_type PERF_SAMPLE_IP to get data->ip.
So I think we may name PERF_SAMPLE_PHYS_IP as the new sample_type
for the physical addresses of IP
Also, since code and data are from different sample_type, I think it may
be better to implement the PERF_SAMPLE_PHYS_IP in a separate patch later.

Thanks,
Kan

>
> Getting code and data physical addresses would provide better coverage
> of the memory subsystem usage.
>
> > Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
> > ---
> > arch/x86/kernel/cpu/perf_event.h | 2 +-
> > arch/x86/kernel/cpu/perf_event_intel_ds.c | 23
> +++++++++++++++++++++++
> > include/linux/perf_event.h | 3 +++
> > include/uapi/linux/perf_event.h | 4 +++-
> > kernel/events/core.c | 11 +++++++++++
> > 5 files changed, 41 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/perf_event.h
> > b/arch/x86/kernel/cpu/perf_event.h
> > index 799e6bd..164de68 100644
> > --- a/arch/x86/kernel/cpu/perf_event.h
> > +++ b/arch/x86/kernel/cpu/perf_event.h
> > @@ -90,7 +90,7 @@ struct amd_nb {
> > (PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR | \
> > PERF_SAMPLE_ID | PERF_SAMPLE_CPU |
> PERF_SAMPLE_STREAM_ID | \
> > PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER | \
> > - PERF_SAMPLE_TRANSACTION)
> > + PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR)
> >
> > /*
> > * A debug store configuration.
> > diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> > b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> > index 5db1c77..2e333dc 100644
> > --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> > @@ -986,6 +986,7 @@ static void setup_pebs_sample_data(struct
> perf_event *event,
> > u64 sample_type;
> > int fll, fst, dsrc;
> > int fl = event->hw.flags;
> > + struct page *p = NULL;
> >
> > if (pebs == NULL)
> > return;
> > @@ -1071,6 +1072,28 @@ static void setup_pebs_sample_data(struct
> perf_event *event,
> > x86_pmu.intel_cap.pebs_format >= 1)
> > data->addr = pebs->dla;
> >
> > + if ((sample_type & PERF_SAMPLE_PHYS_ADDR) && (data->addr !=
> 0)) {
> > + if (data->addr >= TASK_SIZE) {
> > + /* If it's vmalloc()d memory, leave phys_addr as 0 */
> > + if (virt_addr_valid(data->addr) &&
> > + !(data->addr >= VMALLOC_START && data->addr <
> VMALLOC_END))
> > + data->phys_addr = (u64)virt_to_phys((void *)data-
> >addr);
> > + } else {
> > + /*
> > + * Walking the pages tables for user address.
> > + * Interrupts are disabled, so it prevents any tear down
> > + * of the page tables.
> > + * Try IRQ-safe __get_user_pages_fast first.
> > + * If failed, leave phys_addr as 0.
> > + */
> > + if ((current->mm != NULL) &&
> > + (__get_user_pages_fast(data->addr, 1, 0, &p) == 1))
> > + data->phys_addr = page_to_phys(p) +
> > + data->addr % PAGE_SIZE;
> > +
> > + if (p)
> > + put_page(p);
> > + }
> > + }
> > if (x86_pmu.intel_cap.pebs_format >= 2) {
> > /* Only set the TSX weight when no memory weight. */
> > if ((sample_type & PERF_SAMPLE_WEIGHT) && !fll) diff
> > --git a/include/linux/perf_event.h b/include/linux/perf_event.h index
> > f9828a4..d9c0527 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -795,6 +795,8 @@ struct perf_sample_data {
> >
> > struct perf_regs regs_intr;
> > u64 stack_user_size;
> > +
> > + u64 phys_addr;
> > } ____cacheline_aligned;
> >
> > /* default value for data source */
> > @@ -815,6 +817,7 @@ static inline void perf_sample_data_init(struct
> perf_sample_data *data,
> > data->weight = 0;
> > data->data_src.val = PERF_MEM_NA;
> > data->txn = 0;
> > + data->phys_addr = 0;
> > }
> >
> > extern void perf_output_sample(struct perf_output_handle *handle,
> > diff --git a/include/uapi/linux/perf_event.h
> > b/include/uapi/linux/perf_event.h index 1afe962..5afc572 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -139,8 +139,9 @@ enum perf_event_sample_format {
> > PERF_SAMPLE_IDENTIFIER = 1U << 16,
> > PERF_SAMPLE_TRANSACTION = 1U << 17,
> > PERF_SAMPLE_REGS_INTR = 1U << 18,
> > + PERF_SAMPLE_PHYS_ADDR = 1U << 19,
> >
> > - PERF_SAMPLE_MAX = 1U << 19, /* non-ABI */
> > + PERF_SAMPLE_MAX = 1U << 20, /* non-ABI */
> > };
> >
> > /*
> > @@ -767,6 +768,7 @@ enum perf_event_type {
> > * { u64 transaction; } && PERF_SAMPLE_TRANSACTION
> > * { u64 abi; # enum perf_sample_regs_abi
> > * u64 regs[weight(mask)]; } &&
> PERF_SAMPLE_REGS_INTR
> > + * { u64 phys_addr;} && PERF_SAMPLE_PHYS_ADDR
> > * };
> > */
> > PERF_RECORD_SAMPLE = 9,
> > diff --git a/kernel/events/core.c b/kernel/events/core.c index
> > a627f36..9a922a2 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -1334,6 +1334,9 @@ static void __perf_event_header_size(struct
> perf_event *event, u64 sample_type)
> > if (sample_type & PERF_SAMPLE_TRANSACTION)
> > size += sizeof(data->txn);
> >
> > + if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> > + size += sizeof(data->phys_addr);
> > +
> > event->header_size = size;
> > }
> >
> > @@ -5432,6 +5435,9 @@ void perf_output_sample(struct
> perf_output_handle *handle,
> > if (sample_type & PERF_SAMPLE_DATA_SRC)
> > perf_output_put(handle, data->data_src.val);
> >
> > + if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> > + perf_output_put(handle, data->phys_addr);
> > +
> > if (sample_type & PERF_SAMPLE_TRANSACTION)
> > perf_output_put(handle, data->txn);
> >
> > @@ -8269,6 +8275,11 @@ SYSCALL_DEFINE5(perf_event_open,
> > return -EINVAL;
> > }
> >
> > + /* Only privileged users can get kernel addresses */
> > + if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
> > + !capable(CAP_SYS_ADMIN))
> > + return -EACCES;
> > +
> > /*
> > * In cgroup mode, the pid argument is used to pass the fd
> > * opened to the cgroup directory in cgroupfs. The cpu
> > argument
> > --
> > 1.8.3.1
> >

Next message: Alex Williamson: "Re: [PATCH] PCI: Add quirk for Lite-On IT Corp. / Plextor M6e PCI Express"
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