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Message-Id: <20240911-devel-anna-maria-b4-timers-flseep-v2-10-b0d3f33ccfe0@linutronix.de>
Date: Wed, 11 Sep 2024 07:13:36 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: Frederic Weisbecker <frederic@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Jonathan Corbet <corbet@....net>
Cc: linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>,
Dwaipayan Ray <dwaipayanray1@...il.com>
Subject: [PATCH v2 10/15] checkpatch: Remove broken sleep/delay related
checks
checkpatch.pl checks for several things related to sleep and delay
functions. In all warnings the outdated documentation is referenced. All
broken parts are listed one by one in the following with an explanation why
this check is broken. For a basic background of those functions please also
refere to the updated function descriptions of udelay(), nsleep_range() and
msleep().
Be aware: The change is done with a perl knowledge of the level "I'm able
to spell perl".
The following checks are broken:
- Check: (! ($delay < 10) )
Message: "usleep_range is preferred over udelay;
see Documentation/timers/timers-howto.rst\n"
Why is the check broken: When it is an atomic context, udelay() is
mandatory.
- Check: ($min eq $max)
Message: "usleep_range should not use min == max args;
see Documentation/timers/timers-howto.rst\n"
Why is the check broken: When the requested accuracy for the sleep
duration requires it, it is also valid to use
min == max.
- Check: ($delay > 2000)
Message: "long udelay - prefer mdelay;
see arch/arm/include/asm/delay.h\n"
Why is the check broken: The threshold when to start using mdelay() to
prevent an overflow depends on
MAX_UDELAY_MS. This value is architecture
dependent. The used value for the check and
reference is arm specific. Generic would be 5ms,
but this would "break" arm, loongarch and mips
and also the arm value might "break" mips and
loongarch in some configurations.
- Check: ($1 < 20)
Message: "msleep < 20ms can sleep for up to 20ms;
see Documentation/timers/timers-howto.rst\n"
Why is the check broken: msleep(1) might sleep up to 20ms but only on a
HZ=100 system. On a HZ=1000 system this will be
2ms. This means, the threshold cannot be hard
coded as it depends on HZ (jiffy granularity and
timer wheel bucket/level granularity) and also
on the required accuracy of the callsite. See
msleep() and also the USLEEP_RANGE_UPPER_BOUND
value.
Remove all broken checks. Update checkpatch documentation accordingly.
Cc: Andy Whitcroft <apw@...onical.com>
Cc: Joe Perches <joe@...ches.com>
Cc: Dwaipayan Ray <dwaipayanray1@...il.com>
Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
v2: Rephrase commit message
---
Documentation/dev-tools/checkpatch.rst | 6 ------
scripts/checkpatch.pl | 34 ----------------------------------
2 files changed, 40 deletions(-)
diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index a9fac978a525..f5c27be9e673 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -466,12 +466,6 @@ API usage
**UAPI_INCLUDE**
No #include statements in include/uapi should use a uapi/ path.
- **USLEEP_RANGE**
- usleep_range() should be preferred over udelay(). The proper way of
- using usleep_range() is mentioned in the kernel docs.
-
- See: https://www.kernel.org/doc/html/latest/timers/timers-howto.html#delays-information-on-the-various-kernel-delay-sleep-mechanisms
-
Comments
--------
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ba3359bdd1fa..80497da4aaac 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6601,28 +6601,6 @@ sub process {
}
}
-# prefer usleep_range over udelay
- if ($line =~ /\budelay\s*\(\s*(\d+)\s*\)/) {
- my $delay = $1;
- # ignore udelay's < 10, however
- if (! ($delay < 10) ) {
- CHK("USLEEP_RANGE",
- "usleep_range is preferred over udelay; see Documentation/timers/timers-howto.rst\n" . $herecurr);
- }
- if ($delay > 2000) {
- WARN("LONG_UDELAY",
- "long udelay - prefer mdelay; see arch/arm/include/asm/delay.h\n" . $herecurr);
- }
- }
-
-# warn about unexpectedly long msleep's
- if ($line =~ /\bmsleep\s*\((\d+)\);/) {
- if ($1 < 20) {
- WARN("MSLEEP",
- "msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.rst\n" . $herecurr);
- }
- }
-
# check for comparisons of jiffies
if ($line =~ /\bjiffies\s*$Compare|$Compare\s*jiffies\b/) {
WARN("JIFFIES_COMPARISON",
@@ -7079,18 +7057,6 @@ sub process {
}
}
-# check usleep_range arguments
- if ($perl_version_ok &&
- defined $stat &&
- $stat =~ /^\+(?:.*?)\busleep_range\s*\(\s*($FuncArg)\s*,\s*($FuncArg)\s*\)/) {
- my $min = $1;
- my $max = $7;
- if ($min eq $max) {
- WARN("USLEEP_RANGE",
- "usleep_range should not use min == max args; see Documentation/timers/timers-howto.rst\n" . "$here\n$stat\n");
- }
- }
-
# check for naked sscanf
if ($perl_version_ok &&
defined $stat &&
--
2.39.2
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