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.
Add hwpmc(4) support for the PowerPC 970 class processors, direct events.
This also fixes asserts on removal of the module for the mpc74xx.
The PowerPC 970 processors have two different types of events: direct events
and indirect events. Thus far only direct events are supported. I included
some documentation in the driver on how indirect events work, but support is
for the future.
There is no point in hiding, e.g. pmc.xscale(3) from a developer running
on amd64, when the target arch in question will probably never have
manual pages installed at all.
Reviewed by: sbruno, hiren
0x3C: /* Per Intel document 325462-045US 01/2013. */
Add manpage to document all the goodness that is available in this
processor model.
Submitted by: hiren panchasara <hiren.panchasara@gmail.com>
Reviewed by: jimharris, sbruno
Obtained from: Yahoo! Inc.
MFC after: 2 weeks
case 0x3E: /* Per Intel document 325462-045US 01/2013. */
Add manpage to document all the goodness that is available in this
processor model.
No support for uncore events at this time.
Submitted by: hiren panchasara <hiren.panchasara@gmail.com>
Reviewed by: davide, jimharris, sbruno
Obtained from: Yahoo! Inc.
MFC after: 2 weeks
(Model 0x2D /* Per Intel document 253669-044US 08/2012. */)
Add manpage to document all the goodness that is available in this
processor model.
No support for uncore events at this time.
Submitted by: hiren panchasara <hiren.panchasara@gmail.com>
Reviewed by: jimharris@ fabient@
Obtained from: Yahoo! Inc.
MFC after: 2 weeks
New kernel events can be added at various location for sampling or counting.
This will for example allow easy system profiling whatever the processor is
with known tools like pmcstat(8).
Simultaneous usage of software PMC and hardware PMC is possible, for example
looking at the lock acquire failure, page fault while sampling on
instructions.
Sponsored by: NETASQ
MFC after: 1 month
- Rename pmc.mips to pmc.mips24k since it covers just one CPU,
no whole architecture
- Add documetnations for Octeon's PMC counters
- Remove CAVEATS section from pmc.mips24k page: PMC for MIPS supports
sampling now.
o Wrap sentences on to new lines
o Rewrap lines where possible while trying to keep the diff to a
minimum
Found with: textproc/igor
MFC after: 1 week
X-MFC-With: r232157
Advantages:
- Reduces the number of different license versions in the tree
- Eliminates a typo
- Removes some incorrect author attributions due to c/p
- Removes c/p error potential for future pmc manpages
Approved by: jkoshy, gnn, rpaulo, fabient (copyright holders)
MFC after: 1 week
As the underlying block is 4KB if the PMC throughput is low the measurement
will be reported on the next tick. pmcstat(8) use the modified flush API to
reclaim current buffer before displaying next top.
MFC after: 1 month
