sched: Fix "divide error: 0000" in find_busiest_group
PATCH 2/2 sched: Fix "divide error: 0000" in find_busiest_group
Add a check to sched_avg_update() to detect and reset age_stamp if the clock value has wrapped. Because __cycles_2_ns() includes an offset to account for start up time, the clock may not wrap to zero, so use the current clock value instead.
---
kernel/sched.c +2 -0
@@ -1256,6 +1256,8 @@ static void sched_avg_update(struct rq *rq) {s64 period =sched_avg_period (); +if (unlikely (rq->age_stamp > rq->clock)) + rq->age_stamp = rq->clock;while ((s64)(rq->clock - rq->age_stamp) > period) {/* * Inline assembly required to prevent the compiler
Quoted 4 lines · Terry Loftin
Add a check to
sched_avg_update()to detect and resetage_stampif the clock value has wrapped. Because__cycles_2_ns()includes an offset to account for start up time, the clock may not wrap to zero, so use the current clock value instead.
So you're running on a platform (unspecified) where we use a raw sched_clock() that is buggy. Again, you're fixing symptoms not causes.
Quoted 16 lines
Signed-off-by Terry Loftin <[email protected]>Signed-off-by Bob Montgomery <[email protected]>---
kernel/sched.c +2
-0@@ -1256,6 +1256,8 @@ static void sched_avg_update(struct rq *rq) {s64 period =sched_avg_period (); +if (unlikely (rq->age_stamp > rq->clock)) + rq->age_stamp = rq->clock;while ((s64)(rq->clock - rq->age_stamp) > period) {/* * Inline assembly required to prevent the compiler
Quoted 9 lines · Peter Zijlstra
Quoted 4 lines · Terry Loftin
Add a check to
sched_avg_update()to detect and resetage_stampif the clock value has wrapped. Because__cycles_2_ns()includes an offset to account for start up time, the clock may not wrap to zero, so use the current clock value instead.So you're running on a platform (unspecified) where we use a raw
sched_clock()that is buggy. Again, you're fixing symptoms not causes.
This x86_64. This is the actual cause, unless the rq->clock value should never roll, in which case, the clock roll is the actual cause and you can disregard these patches.
-T
Quoted 19 lines
Quoted 16 lines
Signed-off-by Terry Loftin <[email protected]>Signed-off-by Bob Montgomery <[email protected]>---
kernel/sched.c +2
-0@@ -1256,6 +1256,8 @@ static void sched_avg_update(struct rq *rq) {s64 period =sched_avg_period (); +if (unlikely (rq->age_stamp > rq->clock)) + rq->age_stamp = rq->clock;while ((s64)(rq->clock - rq->age_stamp) > period) {/* * Inline assembly required to prevent the compiler
Quoted 6 lines · Terry Loftin
Quoted 3 lines
So you're running on a platform (unspecified) where we use a raw
sched_clock()that is buggy. Again, you're fixing symptoms not causes.This
x86_64. This is the actual cause, unless therq->clockvalue should never roll, in which case, the clock roll is the actual cause and you can disregard these patches.
Its supposed to roll over on the full 64bit, and I think x86_64 only suffers this if you have sched_clock_stable set to 1.
So I think the correct fix is disabling that logic for now. John Stultz was working on some patches to fix __cycles_2_ns().
Something like the below perhaps.
--- arch/x86/kernel/cpu/intel.c | 2 -- 1 files changed, 0 insertions(+), 2 deletions(-)
arch/x86/kernel/cpu/intel.c +0 -2
@@ -91,8 +91,6 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)if (c->x86_power & (1 <<8 )) {set_cpu_cap (c,X86_FEATURE_CONSTANT_TSC );set_cpu_cap (c,X86_FEATURE_NONSTOP_TSC ); -if (!check_tsc_unstable ()) - sched_clock_stable =1 ; }/*
Quoted 8 lines · Peter Zijlstra
Quoted 6 lines · Terry Loftin
Quoted 3 lines
So you're running on a platform (unspecified) where we use a raw
sched_clock()that is buggy. Again, you're fixing symptoms not causes.This
x86_64. This is the actual cause, unless therq->clockvalue should never roll, in which case, the clock roll is the actual cause and you can disregard these patches.
Quoted 7 lines
Its supposed to roll over on the full 64bit, and I think
x86_64only suffers this if you havesched_clock_stableset to 1.So I think the correct fix is disabling that logic for now. John Stultz was working on some patches to fix
__cycles_2_ns().Something like the below perhaps.
OK - this would also avoid the problem I came across. Thank you for your time.
-T
Quoted 20 lines
--- arch/x86/kernel/cpu/intel.c | 2 -- 1 files changed, 0 insertions(+), 2 deletions(-)arch/x86/kernel/cpu/intel.c +0
-2@@ -91,8 +91,6 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)if (c->x86_power & (1 <<8 )) {set_cpu_cap (c,X86_FEATURE_CONSTANT_TSC );set_cpu_cap (c,X86_FEATURE_NONSTOP_TSC ); -if (!check_tsc_unstable ()) - sched_clock_stable =1 ; }/*