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Use strings.Cut where possible #4470
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@kolyshkin I guess this is due to performance? Did you run some numbers or we just tested before this is faster and we are just using strings.Cut in more places? IMHO, it would be nice to say the reason on the commits. If something breaks due to this, it would be nice to know that the commit just changed to this due to performance, so a revert is probably safe until a new fixed version is cooked. But that is not that easy to know if we don't explain why we change it in the commit. |
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Thanks, this makes sense. Individual commit messages as well as this PR description updated; PTAL. |
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@opencontainers/runc-maintainers PTAL. This is a minor cleanup, aiming for more readable and faster code with less allocations. |
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return nil, fmt.Errorf("invalid --cgroup argument: %s", c) | ||
} | ||
if len(cs) == 1 { // no controller: prefix | ||
if ctr, path, ok := strings.Cut(c, ":"); ok { |
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I havn't checked that whether this will lead to some regressions or not, for example, if c == "a:b:c:d:e":
When using SplitN
, cs[1]
will be "b";
When using Cut
, path
will be "b:c:d:e".
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So, the old code would error out when c == "a:b:c:d:e"
.
The new code would not, assigning b:c:d:e
to path
.
To me, the new code is (ever so slightly) more correct, since :
is a valid symbol which should be allowed in path
.
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Yup, was looking at that as well; agreed, looks like new code is more correct here.
I still need to have a quick look at the splitting on commas, and the if len(args) != 1 {
check below. Probably will check out this branch locally
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Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). This part of code is covered by tests in tests/integration/exec.bats. [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
Nowadays strings.Fields are as fast as strings.SplitN so remove TODO. Signed-off-by: Kir Kolyshkin <[email protected]>
Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). This also drops the check for extra dash (we're unlikely to get it from the kernel anyway). While at it, rename min/max -> from/to to avoid collision with Go min/max builtins. This code is tested by TestCPUSetStats* tests. [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
Remove extra global constants that are only used in a single place and make it harder to read the code. Rename nanosecondsInSecond -> nsInSec. This code is tested by unit tests. Signed-off-by: Kir Kolyshkin <[email protected]>
For cgroup v2, we always expect /proc/$PID/cgroup contents like this: > 0::/user.slice/user-1000.slice/[email protected]/app.slice/vte-spawn-f71c3fb8-519d-4e2d-b13e-9252594b1e05.scope So, it does not make sense to parse it using strings.Split, we can just cut the prefix and return the rest. Code tested by TestParseCgroupFromReader. Signed-off-by: Kir Kolyshkin <[email protected]>
Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). The code is tested by testCgroupResourcesUnified. [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). This code is tested by TestStatCPUPSI. [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). Also, use switch in parseRdmaKV. [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
Use strings.Cut in ParseKeyValue and GetValueByKey. Using strings.Cut (added in Go 1.18, see [1]) results in faster and cleaner code with less allocations (as we're not using a slice). [1]: golang/go#46336 Signed-off-by: Kir Kolyshkin <[email protected]>
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usageKernelMode = append(usageKernelMode, kernel) | ||
|
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Accidental empty line added here
fields := strings.SplitN(scanner.Text(), " ", 3) | ||
if len(fields) != 3 { | ||
continue |
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I was considering if we had to check for more than 3 fields to happen here, but I guess that would error already once we try to strconv.ParseUint()
below, so probably not adding anything.
OTOTH, I wonder if there could ever be more columns added here? Old code would do a SplitN(.., 4)
, and would skip if there would be less than 3 or more than 3 columns. The new code would silently skip less than 3 columns, but now errors on more than 3 columns.
Not sure if that behavior was correct, or if it should've processed the first 3 columns (and only ignored the 4th+ columns)? Is there any chance there would ever be more columns added?
if len(parts) < 3 { | ||
return "", fmt.Errorf("invalid cgroup entry: %q", text) | ||
} | ||
// text is like "0::/user.slice/user-1001.slice/session-1.scope" | ||
if parts[0] == "0" && parts[1] == "" { | ||
return parts[2], nil | ||
// "0::/user.slice/user-1001.slice/session-1.scope" | ||
if path, ok := strings.CutPrefix(s.Text(), "0::"); ok { |
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Are we missing an error condition for lines that are invalid? Do we need to handle, say 0:::::::/hello.slice/world.scope
, or is it fine to let those go through?
case "avg10": | ||
pv = &data.Avg10 | ||
case "avg60": | ||
pv = &data.Avg60 | ||
case "avg300": | ||
pv = &data.Avg300 | ||
case "total": | ||
v, err := strconv.ParseUint(kv[1], 10, 64) | ||
v, err := strconv.ParseUint(val, 10, 64) |
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Not for this PR, but I started to look in some other codebases to dismantle these errors. The default error returned is something like;
invalid total PSI value: strconv.ParseUint: parsing "some invalid value": invalid syntax
Which tends to be a bit "implementation detail", and strconv.ParseUint
is not very relevant to the user. So in some cases, dismantling the error can be useful; https://cs.opensource.google/go/go/+/refs/tags/go1.23.4:src/strconv/atoi.go;l=20-49
https://go.dev/play/p/E9Dx1YBzPiN
var numErr *strconv.NumError
if errors.As(err, &numErr) {
fmt.Printf("invalid %s PS value (%s): %w", key, numErr.Num, numErr.Err)
}
Which would be something like;
invalid total PSI value (some invalid value): invalid syntax
|
||
if len(parts) != 2 { | ||
if !ok { | ||
return errors.New("Unable to parse RDMA entry") |
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Some of these could be improved as well; in this case we know it's missing a =
. Wondering if we must also check for empty values after; looks like the if/else
below would fall through to trying to parse empty values as integer, which may produce an obscure error (strconv.ParseUint: parsing "": invalid syntax
).
We could check here if it's empty and return that no value is specified;
if !ok || v == "" {
return errors.New("Unable to parse RDMA entry: no value specified")
}
parts := strings.SplitN(t, " ", 3) | ||
if len(parts) != 2 { | ||
key, val, ok := strings.Cut(t, " ") | ||
if !ok { |
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Not necessarily for this PR, but we could check for empty values here as well to return a nicer error than "strconv.ParseUint failed to parse ...";
if !ok || key == "" || val == "" {
arr := strings.Split(line, " ") | ||
if len(arr) == 2 && arr[0] == key { | ||
val, err := ParseUint(arr[1], 10, 64) | ||
k, v, ok := strings.Cut(line, " ") | ||
if ok && k == key { |
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Not sure if relevant (and probably new code is more correct?); previously, we would ignore cases with more than 2 fields. I.e., key foo bar
would be ignored; in the new code, we'd try to parse foo bar
as value.
That said; see my other comment; this would potentially be an issue if we try to parse something that may currently have 2 cols, and in future 3 cols; not sure if that should error or silently ignore
// No controller: prefix. | ||
if len(args) != 1 { | ||
return nil, fmt.Errorf("invalid --cgroup argument: %s (missing <controller>: prefix)", c) | ||
} | ||
paths[""] = c |
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Was trying to somewhat grasp what this case is for;
- if zero args are passed, we return early (start of function)
- if 1 arg is passed, it MUST have a controller prefix
- But if 2 (or more) args are passed, then we don't have to?
So;
# valid: single arg
--cgroup a,b:/hello-world
# valid: single arg without controller
--cgroup /hello-world
# invalid: multiple args, one without controller
--cgroup a,b:/hello-world --cgroup /hello-world
--cgroup /hello-world --cgroup a,b:/hello-world
So, if no controller is passed, it's for everything which is only allowed if no other (per-controller) paths are specified, correct? (so not allowed to be combined).
☝️ Perhaps that's something we should capture in a comment on the function
Also;
- perhaps we need to change the
ok
check to also check if controller is not empty, or is,,,,,:/hello-world
something that should be considered valid? - are duplicate controllers valid? They currently overwrite previous values (
foo,foo,foo:/bar
,foo:/baz
)
For the most part, this is a switch from
strings.Split[N]
tostrings.Cut
.Using strings.Cut (added in Go 1.18, see 1) results in faster and
cleaner code with less allocations (as we're not using a slice).
There are a few other cleanups and nits here and there.
Please see individual commits for details.