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Message-Id: <20240325064023.2997-19-adrian.hunter@intel.com>
Date: Mon, 25 Mar 2024 08:40:22 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Christophe Leroy <christophe.leroy@...roup.eu>,
"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Vincenzo Frascino <vincenzo.frascino@....com>,
John Stultz <jstultz@...gle.com>,
Stephen Boyd <sboyd@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
linuxppc-dev@...ts.ozlabs.org,
linux-kernel@...r.kernel.org,
linux-s390@...r.kernel.org
Subject: [PATCH V2 18/19] timekeeping: Let timekeeping_cycles_to_ns() handle both under and overflow
For the case !CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE, forego overflow
protection in the range (mask << 1) < delta <= mask, and interpret it
always as an inconsistency between CPU clock values. That allows
slightly neater code, and it is on a slow path so has no effect on
performance.
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
kernel/time/timekeeping.c | 31 +++++++++++++------------------
1 file changed, 13 insertions(+), 18 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 111dfdbd488f..4e18db1819f8 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -266,17 +266,14 @@ static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr)
* Try to catch underflows by checking if we are seeing small
* mask-relative negative values.
*/
- if (unlikely((~delta & mask) < (mask >> 3))) {
+ if (unlikely((~delta & mask) < (mask >> 3)))
tk->underflow_seen = 1;
- now = last;
- }
- /* Cap delta value to the max_cycles values to avoid mult overflows */
- if (unlikely(delta > max)) {
+ /* Check for multiplication overflows */
+ if (unlikely(delta > max))
tk->overflow_seen = 1;
- now = last + max;
- }
+ /* timekeeping_cycles_to_ns() handles both under and overflow */
return timekeeping_cycles_to_ns(tkr, now);
}
#else
@@ -375,19 +372,17 @@ static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 c
u64 mask = tkr->mask, delta = (cycles - tkr->cycle_last) & mask;
/*
- * This detects the case where the delta overflows the multiplication
- * with tkr->mult.
+ * This detects both negative motion and the case where the delta
+ * overflows the multiplication with tkr->mult.
*/
if (unlikely(delta > tkr->clock->max_cycles)) {
- if (IS_ENABLED(CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE)) {
- /*
- * Handle clocksource inconsistency between CPUs to prevent
- * time from going backwards by checking for the MSB of the
- * mask being set in the delta.
- */
- if (unlikely(delta & ~(mask >> 1)))
- return tkr->xtime_nsec >> tkr->shift;
- }
+ /*
+ * Handle clocksource inconsistency between CPUs to prevent
+ * time from going backwards by checking for the MSB of the
+ * mask being set in the delta.
+ */
+ if (delta & ~(mask >> 1))
+ return tkr->xtime_nsec >> tkr->shift;
return delta_to_ns_safe(tkr, delta);
}
--
2.34.1
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