| #
294046 |
|
14-Jan-2016 |
jtl |
MFC r290811:
Fix hwpmc "stalled" behavior
Currently, there is a single pm_stalled flag that tracks whether a
performance monitor was "stalled" due to insufficent ring buffer
space for samples. However, because the same performance monitor
can run on multiple processes or threads at the same time, a single
pm_stalled flag that impacts them all seems insufficient.
In particular, you can hit corner cases where the code fails to stop
performance monitors during a context switch out, because it thinks
the performance monitor is already stopped. However, in reality,
it may be that only the monitor running on a different CPU was stalled.
This patch attempts to fix that behavior by tracking on a per-CPU basis
whether a PM desires to run and whether it is "stalled". This lets the
code make better decisions about when to stop PMs and when to try to
restart them. Ideally, we should avoid the case where the code fails
to stop a PM during a context switch out.
MFC r290813:
Optimizations to the way hwpmc gathers user callchains
Changes to the code to gather user stacks:
* Delay setting pmc_cpumask until we actually have the stack.
* When recording user stack traces, only walk the portion of the ring
that should have samples for us.
MFC r290929:
Change the driver stats to what they really are: unsigned values.
When pmcstat exits after some samples were dropped, give the user an
idea of how many were lost. (Granted, these are global numbers, but
they may still help quantify the scope of the loss.)
MFC r290930:
Improve accuracy of PMC sampling frequency
The code tracks a counter which is the number of events until the next
sample. On context switch in, it loads the saved counter. On context
switch out, it tries to calculate a new saved counter.
Problems:
1. The saved counter was shared by all threads in a process. However, this
means that all threads would be initially loaded with the same saved
counter. However, that could result in sampling more often than once every
X number of events.
2. The calculation to determine a new saved counter was backwards. It
added when it should have subtracted, and subtracted when it should have
added. Assume a single-threaded process with a reload count of 1000
events. Assuming the counter on context switch in was 100 and the counter
on context switch out was 50 (meaning the thread has "consumed" 50 more
events), the code would calculate a new saved counter of 150 (instead of
the proper 50).
Fix:
1. As soon as the saved counter is used to initialize a monitor for a
thread on context switch in, set the saved counter to the reload count.
That way, subsequent threads to use the saved counter will get the full
reload count, assuring we sample at least once every X number of events
(across all threads).
2. Change the calculation of the saved counter. Due to the change to the
saved counter in #1, we simply need to add (modulo the reload count) the
remaining counter time we retrieve from the CPU when a thread is context
switched out.
MFC r291016:
Support a wider history counter in pmcstat(8) gmon output
pmcstat(8) contains an option to output sampling data in a gmon format
compatible with gprof(1). Currently, it uses the default histcounter,
which is an (unsigned short). With large sets of sampling data, it
is possible to overflow the maximum value provided by an (unsigned
short).
This change adds the -e argument to pmcstat. If -e and -g are both
specified, pmcstat will use a histcounter type of uint64_t.
MFC r291017:
Fix the date on the pmcstat(8) man page from r291016.
|
| #
147191 |
|
09-Jun-2005 |
jkoshy |
MFP4:
- Implement sampling modes and logging support in hwpmc(4).
- Separate MI and MD parts of hwpmc(4) and allow sharing of
PMC implementations across different architectures.
Add support for P4 (EMT64) style PMCs to the amd64 code.
- New pmcstat(8) options: -E (exit time counts) -W (counts
every context switch), -R (print log file).
- pmc(3) API changes, improve our ability to keep ABI compatibility
in the future. Add more 'alias' names for commonly used events.
- bug fixes & documentation.
|
| #
145774 |
|
01-May-2005 |
jkoshy |
Add convenience APIs pmc_width() and pmc_capabilities() to -lpmc.
Have pmcstat(8) and pmccontrol(8) use these APIs.
Return PMC class-related constants (PMC widths and capabilities)
with the OP GETCPUINFO call leaving OP PMCINFO to return only the
dynamic information associated with a PMC (i.e., whether enabled,
owner pid, reload count etc.).
Allow pmc_read() (i.e., OPS PMCRW) on active self-attached PMCs to
get upto-date values from hardware since we can guarantee that the
hardware is running the correct PMC at the time of the call.
Bug fixes:
- (x86 class processors) Fix a bug that prevented an RDPMC
instruction from being recognized as permitted till after the
attached process had context switched out and back in again after
a pmc_start() call.
Tighten the rules for using RDPMC class instructions: a GETMSR
OP is now allowed only after an OP ATTACH has been done by the
PMC's owner to itself. OP GETMSR is not allowed for PMCs that
track descendants, for PMCs attached to processes other than
their owner processes.
- (P4/HTT processors only) Fix a bug that caused the MI and MD
layers to get out of sync. Add a new MD operation 'get_config()'
as part of this fix.
- Allow multiple system-mode PMCs at the same row-index but on
different CPUs to be allocated.
- Reject allocation of an administratively disabled PMC.
Misc. code cleanups and refactoring. Improve a few comments.
|