While going over the wakeup code I noticed delayed wakeups only work
for hardware counters but basically all software counters rely on
them.
This patch unifies and generalizes the delayed wakeup to fix this
issue.
Since we're dealing with NMI context bits here, use a cmpxchg() based
single link list implementation to track counters that have pending
wakeups.
[ This should really be generic code for delayed wakeups, but since we
cannot use cmpxchg()/xchg() in generic code, I've let it live in the
perf_counter code. -- Eric Dumazet could use it to aggregate the
network wakeups. ]
Furthermore, the x86 method of using TIF flags was flawed in that its
quite possible to end up setting the bit on the idle task, loosing the
wakeup.
The powerpc method uses per-cpu storage and does appear to be
sufficient.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090330171023.153932974@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: new functionality
Currently, if there are more counters enabled than can fit on the CPU,
the kernel will multiplex the counters on to the hardware using
round-robin scheduling. That isn't too bad for sampling counters, but
for counting counters it means that the value read from a counter
represents some unknown fraction of the true count of events that
occurred while the counter was enabled.
This remedies the situation by keeping track of how long each counter
is enabled for, and how long it is actually on the cpu and counting
events. These times are recorded in nanoseconds using the task clock
for per-task counters and the cpu clock for per-cpu counters.
These values can be supplied to userspace on a read from the counter.
Userspace requests that they be supplied after the counter value by
setting the PERF_FORMAT_TOTAL_TIME_ENABLED and/or
PERF_FORMAT_TOTAL_TIME_RUNNING bits in the hw_event.read_format field
when creating the counter. (There is no way to change the read format
after the counter is created, though it would be possible to add some
way to do that.)
Using this information it is possible for userspace to scale the count
it reads from the counter to get an estimate of the true count:
true_count_estimate = count * total_time_enabled / total_time_running
This also lets userspace detect the situation where the counter never
got to go on the cpu: total_time_running == 0.
This functionality has been requested by the PAPI developers, and will
be generally needed for interpreting the count values from counting
counters correctly.
In the implementation, this keeps 5 time values (in nanoseconds) for
each counter: total_time_enabled and total_time_running are used when
the counter is in state OFF or ERROR and for reporting back to
userspace. When the counter is in state INACTIVE or ACTIVE, it is the
tstamp_enabled, tstamp_running and tstamp_stopped values that are
relevant, and total_time_enabled and total_time_running are determined
from them. (tstamp_stopped is only used in INACTIVE state.) The
reason for doing it like this is that it means that only counters
being enabled or disabled at sched-in and sched-out time need to be
updated. There are no new loops that iterate over all counters to
update total_time_enabled or total_time_running.
This also keeps separate child_total_time_running and
child_total_time_enabled fields that get added in when reporting the
totals to userspace. They are separate fields so that they can be
atomic. We don't want to use atomics for total_time_running,
total_time_enabled etc., because then we would have to use atomic
sequences to update them, which are slower than regular arithmetic and
memory accesses.
It is possible to measure total_time_running by adding a task_clock
counter to each group of counters, and total_time_enabled can be
measured approximately with a top-level task_clock counter (though
inaccuracies will creep in if you need to disable and enable groups
since it is not possible in general to disable/enable the top-level
task_clock counter simultaneously with another group). However, that
adds extra overhead - I measured around 15% increase in the context
switch latency reported by lat_ctx (from lmbench) when a task_clock
counter was added to each of 2 groups, and around 25% increase when a
task_clock counter was added to each of 4 groups. (In both cases a
top-level task-clock counter was also added.)
In contrast, the code added in this commit gives better information
with no overhead that I could measure (in fact in some cases I
measured lower times with this code, but the differences were all less
than one standard deviation).
[ v2: address review comments by Andrew Morton. ]
Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Orig-LKML-Reference: <18890.6578.728637.139402@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: Rework the perfcounter output ABI
use sys_read() only for instant data and provide mmap() output for all
async overflow data.
The first mmap() determines the size of the output buffer. The mmap()
size must be a PAGE_SIZE multiple of 1+pages, where pages must be a
power of 2 or 0. Further mmap()s of the same fd must have the same
size. Once all maps are gone, you can again mmap() with a new size.
In case of 0 extra pages there is no data output and the first page
only contains meta data.
When there are data pages, a poll() event will be generated for each
full page of data. Furthermore, the output is circular. This means
that although 1 page is a valid configuration, its useless, since
we'll start overwriting it the instant we report a full page.
Future work will focus on the output format (currently maintained)
where we'll likey want each entry denoted by a header which includes a
type and length.
Further future work will allow to splice() the fd, also containing the
async overflow data -- splice() would be mutually exclusive with
mmap() of the data.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.470536358@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: new feature giving performance improvement
This adds the ability for userspace to do an mmap on a hardware counter
fd and get access to a read-only page that contains the information
needed to translate a hardware counter value to the full 64-bit
counter value that would be returned by a read on the fd. This is
useful on architectures that allow user programs to read the hardware
counters, such as PowerPC.
The mmap will only succeed if the counter is a hardware counter
monitoring the current process.
On my quad 2.5GHz PowerPC 970MP machine, userspace can read a counter
and translate it to the full 64-bit value in about 30ns using the
mmapped page, compared to about 830ns for the read syscall on the
counter, so this does give a significant performance improvement.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Orig-LKML-Reference: <20090323172417.297057964@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Since the bitfields turned into a bit of a mess, remove them and rely on
good old masks.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.059499915@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: build fix for powerpc
Commit db3a944aca35ae61 ("perf_counter: revamp syscall input ABI")
expanded the hw_event.type field into a union of structs containing
bitfields. In particular it introduced a type field and a raw_type
field, with the intention that the 1-bit raw_type field should
overlay the most-significant bit of the 8-bit type field, and in fact
perf_counter_alloc() now assumes that (or at least, assumes that
raw_type doesn't overlay any of the bits that are 1 in the values of
PERF_TYPE_{HARDWARE,SOFTWARE,TRACEPOINT}).
Unfortunately this is not true on big-endian systems such as PowerPC,
where bitfields are laid out from left to right, i.e. from most
significant bit to least significant. This means that setting
hw_event.type = PERF_TYPE_SOFTWARE will set hw_event.raw_type to 1.
This fixes it by making the layout depend on whether or not
__BIG_ENDIAN_BITFIELD is defined. It's a bit ugly, but that's what
we get for using bitfields in a user/kernel ABI.
Also, that commit didn't fix up some places in arch/powerpc/kernel/
perf_counter.c where hw_event.raw and hw_event.event_id were used.
This fixes them too.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: cleanup
This updates the powerpc perf_counter_interrupt following on from the
"perf_counter: unify irq output code" patch. Since we now use the
generic perf_counter_output code, which sets the perf_counter_pending
flag directly, we no longer need the need_wakeup variable.
This removes need_wakeup and makes perf_counter_interrupt use
get_perf_counter_pending() instead.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Orig-LKML-Reference: <20090319194234.024464535@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: cleanup
Having 3 slightly different copies of the same code around does nobody
any good. First step in revamping the output format.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Orig-LKML-Reference: <20090319194233.929962222@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: modify ABI
The hardware/software classification in hw_event->type became a little
strained due to the addition of tracepoint tracing.
Instead split up the field and provide a type field to explicitly specify
the counter type, while using the event_id field to specify which event to
use.
Raw counters still work as before, only the raw config now goes into
raw_event.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Orig-LKML-Reference: <20090319194233.836807573@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: build fix for powerpc
Commit bd753921015e7905 ("perf_counter: software counter event
infrastructure") introduced a use of TIF_PERF_COUNTERS into the core
perfcounter code. This breaks the build on powerpc because we use
a flag in a per-cpu area to signal wakeups on powerpc rather than
a thread_info flag, because the thread_info flags have to be
manipulated with atomic operations and are thus slower than per-cpu
flags.
This fixes the by changing the core to use an abstracted
set_perf_counter_pending() function, which is defined on x86 to set
the TIF_PERF_COUNTERS flag and on powerpc to set the per-cpu flag
(paca->perf_counter_pending). It changes the previous powerpc
definition of set_perf_counter_pending to not take an argument and
adds a clear_perf_counter_pending, so as to simplify the definition
on x86.
On x86, set_perf_counter_pending() is defined as a macro. Defining
it as a static inline in arch/x86/include/asm/perf_counters.h causes
compile failures because <asm/perf_counters.h> gets included early in
<linux/sched.h>, and the definitions of set_tsk_thread_flag etc. are
therefore not available in <asm/perf_counters.h>. (On powerpc this
problem is avoided by defining set_perf_counter_pending etc. in
<asm/hw_irq.h>.)
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: more hardware support
This adds the back-end for the PMU on the POWER4 and POWER4+ processors
(GP and GQ). This is quite similar to the PPC970, with 8 PMCs, but has
fewer events than the PPC970.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: more hardware support
This adds the back-end for the PMU on the POWER5+ processors (i.e. GS,
including GS DD3 aka POWER5++). This doesn't use the fixed-function
PMC5 and PMC6 since they don't respect the freeze conditions and don't
generate interrupts, as on POWER6.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: fix oops-causing bug
This fixes a bug in the powerpc hw_perf_counter_init where the code
didn't initialize ctrs[n] before passing the ctrs array to check_excludes,
leading to possible oopses and other incorrect behaviour. This fixes it
by initializing ctrs[n] correctly.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This adds the back-end for the PMU on the POWER5 processor. This knows
how to use the fixed-function PMC5 and PMC6 (instructions completed and
run cycles). Unlike POWER6, PMC5/6 obey the freeze conditions and can
generate interrupts, so their use doesn't impose any extra restrictions.
POWER5+ is different and is not supported by this patch.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Currently, setting hw_event.exclude_kernel does nothing on the PPC970
variants used in Apple G5 machines, because they have the HV (hypervisor)
bit in the MSR forced to 1, so as far as the PMU is concerned, the
kernel runs in hypervisor mode. Thus we have to use the MMCR0_FCHV
(freeze counters in hypervisor mode) bit rather than the MMCR0_FCS
(freeze counters in supervisor mode) bit.
This checks the MSR.HV bit at startup, and if it is set, we set the
freeze_counters_kernel variable to MMCR0_FCHV (it was initialized to
MMCR0_FCS). We then use that whenever we need to exclude kernel events.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: new perf_counter feature
This extends the perf_counter_hw_event struct with bits that specify
that events in user, kernel and/or hypervisor mode should not be
counted (i.e. should be excluded), and adds code to program the PMU
mode selection bits accordingly on x86 and powerpc.
For software counters, we don't currently have the infrastructure to
distinguish which mode an event occurs in, so we currently fail the
counter initialization if the setting of the hw_event.exclude_* bits
would require us to distinguish. Context switches and CPU migrations
are currently considered to occur in kernel mode.
On x86, this changes the previous policy that only root can count
kernel events. Now non-root users can count kernel events or exclude
them. Non-root users still can't use NMI events, though. On x86 we
don't appear to have any way to control whether hypervisor events are
counted or not, so hw_event.exclude_hv is ignored.
On powerpc, the selection of whether to count events in user, kernel
and/or hypervisor mode is PMU-wide, not per-counter, so this adds a
check that the hw_event.exclude_* settings are the same as other events
on the PMU. Counters being added to a group have to have the same
settings as the other hardware counters in the group. Counters and
groups can only be enabled in hw_perf_group_sched_in or power_perf_enable
if they have the same settings as any other counters already on the
PMU. If we are not running on a hypervisor, the exclude_hv setting
is ignored (by forcing it to 0) since we can't ever get any
hypervisor events.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: New perf_counter features
A pinned counter group is one that the user wants to have on the CPU
whenever possible, i.e. whenever the associated task is running, for
a per-task group, or always for a per-cpu group. If the system
cannot satisfy that, it puts the group into an error state where
it is not scheduled any more and reads from it return EOF (i.e. 0
bytes read). The group can be released from error state and made
readable again using prctl(PR_TASK_PERF_COUNTERS_ENABLE). When we
have finer-grained enable/disable controls on counters we'll be able
to reset the error state on individual groups.
An exclusive group is one that the user wants to be the only group
using the CPU performance monitor hardware whenever it is on. The
counter group scheduler will not schedule an exclusive group if there
are already other groups on the CPU and will not schedule other groups
onto the CPU if there is an exclusive group scheduled (that statement
does not apply to groups containing only software counters, which can
always go on and which do not prevent an exclusive group from going on).
With an exclusive group, we will be able to let users program PMU
registers at a low level without the concern that those settings will
perturb other measurements.
Along the way this reorganizes things a little:
- is_software_counter() is moved to perf_counter.h.
- cpuctx->active_oncpu now records the number of hardware counters on
the CPU, i.e. it now excludes software counters. Nothing was reading
cpuctx->active_oncpu before, so this change is harmless.
- A new cpuctx->exclusive field records whether we currently have an
exclusive group on the CPU.
- counter_sched_out moves higher up in perf_counter.c and gets called
from __perf_counter_remove_from_context and __perf_counter_exit_task,
where we used to have essentially the same code.
- __perf_counter_sched_in now goes through the counter list twice, doing
the pinned counters in the first loop and the non-pinned counters in
the second loop, in order to give the pinned counters the best chance
to be scheduled in.
Note that only a group leader can be exclusive or pinned, and that
attribute applies to the whole group. This avoids some awkwardness in
some corner cases (e.g. where a group leader is closed and the other
group members get added to the context list). If we want to relax that
restriction later, we can, and it is easier to relax a restriction than
to apply a new one.
This doesn't yet handle the case where a pinned counter is inherited
and goes into error state in the child - the error state is not
propagated up to the parent when the child exits, and arguably it
should.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This makes sure that we call the platform-specific ppc_md.enable_pmcs
function on each CPU before we try to use the PMU on that CPU. If the
CPU goes off-line and then on-line, we need to do the enable_pmcs call
again, so we use the hw_perf_counter_setup hook to ensure that. It gets
called as each CPU comes online, but it isn't called on the CPU that is
coming up, so this adds the CPU number as an argument to it (there were
no non-empty instances of hw_perf_counter_setup before).
This also arranges to set the pmcregs_in_use field of the lppaca (data
structure shared with the hypervisor) on each CPU when we are using the
PMU and clear it when we are not. This allows the hypervisor to optimize
partition switches by not saving/restoring the PMU registers when we
aren't using the PMU.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This adds the back-end for the PMU on the POWER6 processor.
Fortunately, the event selection hardware is somewhat simpler on
POWER6 than on other POWER family processors, so the constraints
fit into only 32 bits.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This adds the back-end for the PMU on the PPC970 family.
The PPC970 allows events from the ISU to be selected in two different
ways. Rather than use alternative event codes to express this, we
instead use a single encoding for ISU events and express the
resulting constraint (that you can't select events from all three
of FPU/IFU/VPU, ISU and IDU/STS at the same time, since they all come
in through only 2 multiplexers) using a NAND constraint field, and
work out which multiplexer is used for ISU events at compute_mmcr
time.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This provides the architecture-specific functions needed to access
PMU hardware on the 64-bit PowerPC processors. It has been designed
for the IBM POWER family (POWER 4/4+/5/5+/6 and PPC970) but will
hopefully also suit other 64-bit PowerPC machines (although probably
not Cell given how different it is in this area). This doesn't
include back-ends for any specific processors.
This implements a system which allows back-ends to express the
constraints that their hardware has on what events can be counted
simultaneously. The constraints are expressed as a 64-bit mask +
64-bit value for each event, and the encoding is capable of
expressing the constraints arising from having a set of multiplexers
feeding an event bus, with some events being available through
multiple multiplexer settings, such as we get on POWER4 and PPC970.
Furthermore, the back-end can supply alternative event codes for
each event, and the constraint checking code will try all possible
combinations of alternative event codes to try to find a combination
that will fit.
Signed-off-by: Paul Mackerras <paulus@samba.org>
