-
Notifications
You must be signed in to change notification settings - Fork 1.9k
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
metrics: prevent negative counter from iowait decrease (backport 1.6.x) #18849
Merged
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
The iowait metric obtained from `/proc/stat` can under some circumstances decrease. The relevant condition is when an interrupt arrives on a different core than the one that gets woken up for the IO, and a particular counter in the kernel for that core gets interrupted. This is documented in the man page for the `proc(5)` pseudo-filesystem, and considered an unfortunate behavior that can't be changed for the sake of ABI compatibility. In Nomad, we get the current "busy" time (everything except for idle) and compare it to the previous busy time to get the counter incremeent. If the iowait counter decreases and the idle counter increases more than the increase in the total busy time, we can get a negative total. This previously caused a panic in our metrics collection (see #15861) but that is being prevented by reporting an error message. Fix the bug by putting a zero floor on the values we return from the host CPU stats calculator. Backport-of: #18835
shoenig
approved these changes
Oct 24, 2023
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
LGTM!
tgross
added a commit
that referenced
this pull request
Oct 24, 2023
The iowait metric obtained from `/proc/stat` can under some circumstances decrease. The relevant condition is when an interrupt arrives on a different core than the one that gets woken up for the IO, and a particular counter in the kernel for that core gets interrupted. This is documented in the man page for the `proc(5)` pseudo-filesystem, and considered an unfortunate behavior that can't be changed for the sake of ABI compatibility. In Nomad, we get the current "busy" time (everything except for idle) and compare it to the previous busy time to get the counter incremeent. If the iowait counter decreases and the idle counter increases more than the increase in the total busy time, we can get a negative total. This previously caused a panic in our metrics collection (see #15861) but that is being prevented by reporting an error message. Fix the bug by putting a zero floor on the values we return from the host CPU stats calculator. Backport-of: #18835
tgross
added a commit
that referenced
this pull request
Oct 24, 2023
The iowait metric obtained from `/proc/stat` can under some circumstances decrease. The relevant condition is when an interrupt arrives on a different core than the one that gets woken up for the IO, and a particular counter in the kernel for that core gets interrupted. This is documented in the man page for the `proc(5)` pseudo-filesystem, and considered an unfortunate behavior that can't be changed for the sake of ABI compatibility. In Nomad, we get the current "busy" time (everything except for idle) and compare it to the previous busy time to get the counter incremeent. If the iowait counter decreases and the idle counter increases more than the increase in the total busy time, we can get a negative total. This previously caused a panic in our metrics collection (see #15861) but that is being prevented by reporting an error message. Fix the bug by putting a zero floor on the values we return from the host CPU stats calculator. Backport-of: #18835
Backported manually to 1.5.x and 1.4.x. |
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.
The iowait metric obtained from
/proc/stat
can under some circumstances decrease. The relevant condition is when an interrupt arrives on a different core than the one that gets woken up for the IO, and a particular counter in the kernel for that core gets interrupted. This is documented in the man page for theproc(5)
pseudo-filesystem, and considered an unfortunate behavior that can't be changed for the sake of ABI compatibility.In Nomad, we get the current "busy" time (everything except for idle) and compare it to the previous busy time to get the counter incremeent. If the iowait counter decreases and the idle counter increases more than the increase in the total busy time, we can get a negative total. This previously caused a panic in our metrics collection (see #15861) but that is being prevented by reporting an error message.
Fix the bug by putting a zero floor on the values we return from the host CPU stats calculator.
Backport-of: #18835 (the code touched here was moved, so this backport had to be done by hand)