[−][src]Struct nc::types::perf_event_mmap_page_t
Structure of the page that can be mapped via mmap
Fields
version: u32
version number of this structure
compat_version: u32
lowest version this is compat with
lock: u32
Bits needed to read the hw events in user-space.
u32 seq, time_mult, time_shift, index, width;
u64 count, enabled, running;
u64 cyc, time_offset;
s64 pmc = 0;
do {
seq = pc->lock;
barrier()
enabled = pc->time_enabled;
running = pc->time_running;
if (pc->cap_usr_time && enabled != running) {
cyc = rdtsc();
time_offset = pc->time_offset;
time_mult = pc->time_mult;
time_shift = pc->time_shift;
}
index = pc->index;
count = pc->offset;
if (pc->cap_user_rdpmc && index) {
width = pc->pmc_width;
pmc = rdpmc(index - 1);
}
barrier();
} while (pc->lock != seq);
NOTE: for obvious reason this only works on self-monitoring processes. seqlock for synchronization
index: u32
hardware event identifier
offset: i64
add to hardware event value
time_enabled: u64
time event active
time_running: u64
time event on cpu
cap: perf_event_mmap_page_cap_t
pmc_width: u16
If cap_user_rdpmc this field provides the bit-width of the value read using the rdpmc() or equivalent instruction. This can be used to sign extend the result like:
pmc <<= 64 - width; pmc >>= 64 - width; // signed shift right count += pmc;
time_shift: u16
If cap_usr_time the below fields can be used to compute the time delta since time_enabled (in ns) using rdtsc or similar.
u64 quot, rem; u64 delta;
quot = (cyc >> time_shift); rem = cyc & (((u64)1 << time_shift) - 1); delta = time_offset + quot * time_mult + ((rem * time_mult) >> time_shift);
Where time_offset,time_mult,time_shift and cyc are read in the seqcount loop described above. This delta can then be added to enabled and possible running (if index), improving the scaling:
enabled += delta; if (index) running += delta;
quot = count / running; rem = count % running; count = quot * enabled + (rem * enabled) / running;
time_mult: u32
time_offset: u64
time_zero: u64
If cap_usr_time_zero, the hardware clock (e.g. TSC) can be calculated from sample timestamps.
time = timestamp - time_zero; quot = time / time_mult; rem = time % time_mult; cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
And vice versa:
quot = cyc >> time_shift; rem = cyc & (((u64)1 << time_shift) - 1); timestamp = time_zero + quot * time_mult + ((rem * time_mult) >> time_shift);
size: u32
Header size up to __reserved[] fields.
data_head: u64
Control data for the mmap() data buffer.
User-space reading the @data_head value should issue an smp_rmb() after reading this value.
When the mapping is PROT_WRITE the @data_tail value should be written by userspace to reflect the last read data, after issueing an smp_mb() to separate the data read from the ->data_tail store. In this case the kernel will not over-write unread data.
See perf_output_put_handle() for the data ordering.
data_{offset,size} indicate the location and size of the perf record buffer within the mmapped area. head in the data section
data_tail: u64
user-space written tail
data_offset: u64
where the buffer starts
data_size: u64
data buffer size
aux_head: u64
AUX area is defined by aux_{offset,size} fields that should be set by the userspace, so that
aux_offset >= data_offset + data_size
prior to mmap()ing it. Size of the mmap()ed area should be aux_size.
Ring buffer pointers aux_{head,tail} have the same semantics as data_{head,tail} and same ordering rules apply.
aux_tail: u64
aux_offset: u64
aux_size: u64
Auto Trait Implementations
impl Unpin for perf_event_mmap_page_t
impl Send for perf_event_mmap_page_t
impl Sync for perf_event_mmap_page_t
Blanket Implementations
impl<T> From<T> for T
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impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,