From: "Paul E. McKenney" <paulmck@kernel.org>
To: tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org,
sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com,
maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org,
ak@linux.intel.com, "Paul E. McKenney" <paulmck@kernel.org>,
Chris Mason <clm@fb.com>
Subject: [PATCH v9 clocksource 4/6] clocksource: Provide a module parameter to fuzz per-CPU clock checking
Date: Sun, 18 Apr 2021 21:52:58 -0700 [thread overview]
Message-ID: <20210419045300.596332-4-paulmck@kernel.org> (raw)
In-Reply-To: <20210419045155.GA596058@paulmck-ThinkPad-P17-Gen-1>
Code that checks for clock desynchronization must itself be tested, so
create a new clocksource.inject_delay_shift_percpu= kernel boot parameter
that adds or subtracts a large value from the check read, using the
specified bit of the CPU ID to determine whether to add or to subtract.
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mark Rutland <Mark.Rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Reported-by: Chris Mason <clm@fb.com>
[ paulmck: Apply Randy Dunlap feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 16 ++++++++++++++++
kernel/time/clocksource.c | 10 +++++++++-
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7fff95bd5504..03a8c88a6bb9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -599,6 +599,22 @@
will be five delay-free reads followed by three
delayed reads.
+ clocksource.inject_delay_shift_percpu= [KNL]
+ Clocksource delay injection partitions the CPUs
+ into two sets, one whose clocks are moved ahead
+ and the other whose clocks are moved behind.
+ This kernel parameter selects the CPU-number
+ bit that determines which of these two sets the
+ corresponding CPU is placed into. For example,
+ setting this parameter to the value 4 will result
+ in the first set containing alternating groups
+ of 16 CPUs whose clocks are moved ahead, while
+ the second set will contain the rest of the CPUs,
+ whose clocks are moved behind.
+
+ The default value of -1 disables this type of
+ error injection.
+
clocksource.max_read_retries= [KNL]
Number of clocksource_watchdog() retries due to
external delays before the clock will be marked
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index ee33f14be44d..edcff9fc3f44 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -196,6 +196,8 @@ static ulong inject_delay_period;
module_param(inject_delay_period, ulong, 0644);
static ulong inject_delay_repeat = 1;
module_param(inject_delay_repeat, ulong, 0644);
+static int inject_delay_shift_percpu = -1;
+module_param(inject_delay_shift_percpu, int, 0644);
static ulong max_read_retries = 3;
module_param(max_read_retries, ulong, 0644);
@@ -252,8 +254,14 @@ static cpumask_t cpus_behind;
static void clocksource_verify_one_cpu(void *csin)
{
struct clocksource *cs = (struct clocksource *)csin;
+ s64 delta = 0;
+ int sign;
- csnow_mid = cs->read(cs);
+ if (inject_delay_shift_percpu >= 0) {
+ sign = ((smp_processor_id() >> inject_delay_shift_percpu) & 0x1) * 2 - 1;
+ delta = sign * NSEC_PER_SEC;
+ }
+ csnow_mid = cs->read(cs) + delta;
}
static void clocksource_verify_percpu(struct clocksource *cs)
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2021-04-19 4:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-19 4:51 [PATCH v9 clocksource 0/6] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-19 4:52 ` [PATCH v9 clocksource 1/6] clocksource: Provide module parameters to inject delays in watchdog Paul E. McKenney
2021-04-19 4:52 ` [PATCH v9 clocksource 2/6] clocksource: Retry clock read if long delays detected Paul E. McKenney
2021-04-19 4:52 ` [PATCH v9 clocksource 3/6] clocksource: Check per-CPU clock synchronization when marked unstable Paul E. McKenney
2021-04-19 4:52 ` Paul E. McKenney [this message]
2021-04-19 4:52 ` [PATCH v9 clocksource 5/6] clocksource: Limit number of CPUs checked for clock synchronization Paul E. McKenney
2021-04-19 4:53 ` [PATCH v9 clocksource 6/6] clocksource: Reduce WATCHDOG_THRESHOLD Paul E. McKenney
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