Fallback to software cpu-clock-ticks if cpu-cycles is not supported #2816
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
In the next commit it will be used in one more place, so deduplicate the code Signed-off-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
Some machines, mainly VMs, may lack hardware support for cpu-cycles counter. However, it is no reason not to support them: there may be a similar software event available: PERF_COUNT_SW_CPU_CLOCK. The idea is taken from the kernel-provided `perf` utility, function `evsel__fallback` at evsel.c file. Fixes: rr-debugger#2815, rr-debugger#1753 Signed-off-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
Hi-Angel
force-pushed
the
fix-sw-events
branch
from
75b6eb7
to
cbd30f0
Compare
|
upd: fixed a commit title |
This was referenced Feb 20, 2021
|
We don't want to do this. rr can't work without working hardware performance counters, and if the cycle counter doesn't work, the retired-conditional-branches counter inevitably won't work either. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Some machines, mainly VMs, may lack hardware support for cpu-cycles counter. However, it is no reason not to support them: there may be a similar software event available: PERF_COUNT_SW_CPU_CLOCK.
The idea is taken from the kernel-provided
perfutility, functionevsel__fallbackat evsel.c file.Fixes: #2815, #1753
Note: although #1753 is closed, but it has same underlying problem as 2815, so I think it's fair to say this PR fixes both of issues.
Another thing worth noting: I said at this comment that I couldn't test it because I stumbled upon an irrelevant problem. That problem I still have, but it is clearly a separate issue. To test that my changes work as expected I simply hardcoded them in place of the hw events, and ran
rr record echo heywithrr replayon my laptop. No problems were experienced.