https://github.com/torvalds/linux
Revision f792565326825ed806626da50c6f9a928f1079c1 authored by Song Liu on 29 September 2021, 19:43:13 UTC, committed by Peter Zijlstra on 01 October 2021, 11:57:54 UTC
Users of rdpmc rely on the mmapped user page to calculate accurate
time_enabled. Currently, userpage->time_enabled is only updated when the
event is added to the pmu. As a result, inactive event (due to counter
multiplexing) does not have accurate userpage->time_enabled. This can
be reproduced with something like:
/* open 20 task perf_event "cycles", to create multiplexing */
fd = perf_event_open(); /* open task perf_event "cycles" */
userpage = mmap(fd); /* use mmap and rdmpc */
while (true) {
time_enabled_mmap = xxx; /* use logic in perf_event_mmap_page */
time_enabled_read = read(fd).time_enabled;
if (time_enabled_mmap > time_enabled_read)
BUG();
}
Fix this by updating userpage for inactive events in merge_sched_in.
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-and-tested-by: Lucian Grijincu <lucian@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210929194313.2398474-1-songliubraving@fb.com
1 parent ecc2123
Tip revision: f792565326825ed806626da50c6f9a928f1079c1 authored by Song Liu on 29 September 2021, 19:43:13 UTC
perf/core: fix userpage->time_enabled of inactive events
perf/core: fix userpage->time_enabled of inactive events
Tip revision: f792565
| File | Mode | Size |
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| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | -rw-r--r-- | 16.6 KB |
| .cocciconfig | -rw-r--r-- | 59 bytes |
| .get_maintainer.ignore | -rw-r--r-- | 71 bytes |
| .gitattributes | -rw-r--r-- | 62 bytes |
| .gitignore | -rw-r--r-- | 1.9 KB |
| .mailmap | -rw-r--r-- | 19.8 KB |
| COPYING | -rw-r--r-- | 496 bytes |
| CREDITS | -rw-r--r-- | 98.6 KB |
| Kbuild | -rw-r--r-- | 1.3 KB |
| Kconfig | -rw-r--r-- | 555 bytes |
| MAINTAINERS | -rw-r--r-- | 605.7 KB |
| Makefile | -rw-r--r-- | 64.0 KB |
| README | -rw-r--r-- | 727 bytes |
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