Revision c8b947642d2339ce74c6a1ce56726089539f48d9 authored by James Clark on 28 October 2021, 13:48:25 UTC, committed by Arnaldo Carvalho de Melo on 13 November 2021, 21:11:51 UTC
Currently the test skips with an error because == only works in bash:
$ ./perf test 91 -v
Couldn't bump rlimit(MEMLOCK), failures may take place when creating BPF maps, etc
91: perf stat --bpf-counters test :
--- start ---
test child forked, pid 44586
./tests/shell/stat_bpf_counters.sh: 26: [: -v: unexpected operator
test child finished with -2
---- end ----
perf stat --bpf-counters test: Skip
Changing == to = does the same thing, but doesn't result in an error:
./perf test 91 -v
Couldn't bump rlimit(MEMLOCK), failures may take place when creating BPF maps, etc
91: perf stat --bpf-counters test :
--- start ---
test child forked, pid 45833
Skipping: --bpf-counters not supported
Error: unknown option `bpf-counters'
[...]
test child finished with -2
---- end ----
perf stat --bpf-counters test: Skip
Signed-off-by: James Clark <james.clark@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20211028134828.65774-2-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
1 parent 88e4823
atomic_bitops.txt
=============
Atomic bitops
=============
While our bitmap_{}() functions are non-atomic, we have a number of operations
operating on single bits in a bitmap that are atomic.
API
---
The single bit operations are:
Non-RMW ops:
test_bit()
RMW atomic operations without return value:
{set,clear,change}_bit()
clear_bit_unlock()
RMW atomic operations with return value:
test_and_{set,clear,change}_bit()
test_and_set_bit_lock()
Barriers:
smp_mb__{before,after}_atomic()
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
SEMANTICS
---------
Non-atomic ops:
In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.
RMW ops:
The test_and_{}_bit() operations return the original value of the bit.
ORDERING
--------
Like with atomic_t, the rule of thumb is:
- non-RMW operations are unordered;
- RMW operations that have no return value are unordered;
- RMW operations that have a return value are fully ordered.
- RMW operations that are conditional are unordered on FAILURE,
otherwise the above rules apply. In the case of test_and_{}_bit() operations,
if the bit in memory is unchanged by the operation then it is deemed to have
failed.
Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
clear_bit_unlock() which has RELEASE semantics.
Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.
Computing file changes ...
