Power8 has a new register (MMCR2), which contains individual freeze bits
for each counter. This is an improvement on previous chips as it means
we can have multiple events on the PMU at the same time with different
exclude_{user,kernel,hv} settings. Previously we had to ensure all
events on the PMU had the same exclude settings.
The core of the patch is fairly simple. We use the 207S feature flag to
indicate that the PMU backend supports per-event excludes, if it's set
we skip the generic logic that enforces the equality of excludes between
events. We also use that flag to skip setting the freeze bits in MMCR0,
the PMU backend is expected to have handled setting them in MMCR2.
The complication arises with EBB. The FCxP bits in MMCR2 are accessible
R/W to a task using EBB. Which means a task using EBB will be able to
see that we are using MMCR2 for freezing, whereas the old logic which
used MMCR0 is not user visible.
The task can not see or affect exclude_kernel & exclude_hv, so we only
need to consider exclude_user.
The table below summarises the behaviour both before and after this
commit is applied:
exclude_user true false
------------------------------------
| User visible | N N
Before | Can freeze | Y Y
| Can unfreeze | N Y
------------------------------------
| User visible | Y Y
After | Can freeze | Y Y
| Can unfreeze | Y/N Y
------------------------------------
So firstly I assert that the simple visibility of the exclude_user
setting in MMCR2 is a non-issue. The event belongs to the task, and
was most likely created by the task. So the exclude_user setting is not
privileged information in any way.
Secondly, the behaviour in the exclude_user = false case is unchanged.
This is important as it is the case that is actually useful, ie. the
event is created with no exclude setting and the task uses MMCR2 to
implement exclusion manually.
For exclude_user = true there is no meaningful change to freezing the
event. Previously the task could use MMCR2 to freeze the event, though
it was already frozen with MMCR0. With the new code the task can use
MMCR2 to freeze the event, though it was already frozen with MMCR2.
The only real change is when exclude_user = true and the task tries to
use MMCR2 to unfreeze the event. Previously this had no effect, because
the event was already frozen in MMCR0. With the new code the task can
unfreeze the event in MMCR2, but at some indeterminate time in the
future the kernel will overwrite its setting and refreeze the event.
Therefore my final assertion is that any task using exclude_user = true
and also fiddling with MMCR2 was deeply confused before this change, and
remains so after it.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To support per-event exclude settings on Power8 we need access to the
struct perf_events in compute_mmcr().
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Instead of separate bits for every POWER8 PMU feature, have a single one
for v2.07 of the architecture.
This saves us adding a MMCR2 define for a future patch.
Cc: stable@vger.kernel.org
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Currently we reject events which have the L3 bank == 1, such as
0x000084918F, because the cache field is non-zero.
However that is incorrect, because although the bank is non-zero, the
value we would write into MMCRC is zero, and so we can count the event.
So fix the check to ignore the bank selector when checking whether the
cache selector is non-zero.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We want a way for users of EBB (Event Based Branches) to also access the
BHRB (Branch History Rolling Buffer). EBB does not interoperate with our
existing BHRB support, which is wired into the generic Linux branch
stack sampling support.
To support EBB & BHRB we add three new bits to the event code. The first
bit indicates that the event wants access to the BHRB, and the other two
bits indicate the desired IFM (Instruction Filtering Mode).
We allow multiple events to request access to the BHRB, but they must
agree on the IFM value. Events which are not interested in the BHRB can
also interoperate with events which do.
Finally we program the desired IFM value into MMCRA. Although we do this
for every event, we know that the value will be identical for all events
that request BHRB access.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We only need to mask the EBB bit out of the event for the check of the
special PMC 5 & 6 events. So use a local to do it just for that code,
rather than changing the event value for the life of the function.
While we're there move the set of mask and value after all the checks.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Rather than using PERF_EVENT_CONFIG_EBB_SHIFT everywhere, add an
EVENT_EBB_SHIFT like every other event and use that.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Some power8 revisions have a hardware bug where we can lose a PMU
exception, this commit adds a workaround to detect the bad condition and
rectify the situation.
See the comment in the commit for a full description.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Commit 4df4899 "Add power8 EBB support" included a bug in the handling
of the FAB_CRESP_MATCH and FAB_TYPE_MATCH fields.
These values are pulled out of the event code using EVENT_THR_CTL_SHIFT,
however we were then or'ing that value directly into MMCR1.
This meant we were failing to set the FAB fields correctly, and also
potentially corrupting the value for PMC4SEL. Leading to no counts for
the FAB events and incorrect counts for PMC4.
The fix is simply to shift left the FAB value correctly before or'ing it
with MMCR1.
Reported-by: Sooraj Ravindran Nair <soonair3@in.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We use bit 63 of the event code for userspace to request that the event
be counted using EBB (Event Based Branches). Export this value, making
it part of the API - though only on processors that support EBB.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Completely ignore BHRB privilege state filter request as we are
already configuring that with privilege state filtering attribute
for the accompanying PMU event. This would help achieve cleaner
user space interaction for BHRB.
This patch fixes a situation like this
Before patch:-
------------
./perf record -j any -e branch-misses:k ls
Error:
The sys_perf_event_open() syscall returned with 95 (Operation not
supported) for event (branch-misses:k).
/bin/dmesg may provide additional information.
No CONFIG_PERF_EVENTS=y kernel support configured?
Here 'perf record' actually copies over ':k' filter request into BHRB
privilege state filter config and our previous check in kernel would
fail that.
After patch:-
-------------
./perf record -j any -e branch-misses:k ls
perf perf.data perf.data.old test-mmap-ring
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.002 MB perf.data (~102 samples)]
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
The presence or absence of EBB is advertised to userspace via the presence
or absence of PPC_FEATURE2_EBB in cpu_user_features2.
Because the kernel can be built without PMU support, we should only add
PPC_FEATURE2_EBB to cpu_user_features2 when we successfully register the
power8 PMU support.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Add logic to the power8 PMU code to support EBB. Future processors would
also be expected to implement similar constraints. At that time we could
possibly factor these out into common code.
Finally mark the power8 PMU as supporting EBB, which is the actual
enable switch which allows EBBs to be configured.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
On Power8 we can freeze PMC5 and 6 if we're not using them. Normally they
run all the time.
As noticed by Anshuman, we should unfreeze them when we disable the PMU
as there are legacy tools which expect them to run all the time.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
CC: <stable@vger.kernel.org> [v3.10]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
A mistake we have made in the past is that we pull out the fields we
need from the event code, but don't check that there are no unknown bits
set. This means that we can't ever assign meaning to those unknown bits
in future.
Although we have once again failed to do this at release, it is still
early days for Power8 so I think we can still slip this in and get away
with it.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
CC: <stable@vger.kernel.org> [v3.10]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This patch populates BHRB specific data for power_pmu structure. It
also implements POWER8 specific BHRB filter and configuration functions.
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This patch adds support for the power8 PMU to perf.
Work is ongoing to add generic cache events.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Michael Ellerman