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author | Peter Zijlstra <peterz@infradead.org> | 2013-11-19 16:13:38 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2014-01-13 17:39:11 +0100 |
commit | 37089834528be3ef8cbf927e47c753b3e272a856 (patch) | |
tree | 9cce66ba40e5c0684b3e4f4f354dd717aa1fef84 /include/net/busy_poll.h | |
parent | 1774e9f3e5c8b38de3b3bc8bd0eacd280f655baf (diff) | |
download | linux-stable-37089834528be3ef8cbf927e47c753b3e272a856.tar.gz linux-stable-37089834528be3ef8cbf927e47c753b3e272a856.tar.bz2 linux-stable-37089834528be3ef8cbf927e47c753b3e272a856.zip |
sched, net: Fixup busy_loop_us_clock()
The only valid use of preempt_enable_no_resched() is if the very next
line is schedule() or if we know preemption cannot actually be enabled
by that statement due to known more preempt_count 'refs'.
This busy_poll stuff looks to be completely and utterly broken,
sched_clock() can return utter garbage with interrupts enabled (rare
but still) and it can drift unbounded between CPUs.
This means that if you get preempted/migrated and your new CPU is
years behind on the previous CPU we get to busy spin for a _very_ long
time.
There is a _REASON_ sched_clock() warns about preemptability -
papering over it with a preempt_disable()/preempt_enable_no_resched()
is just terminal brain damage on so many levels.
Replace sched_clock() usage with local_clock() which has a bounded
drift between CPUs (<2 jiffies).
There is a further problem with the entire busy wait poll thing in
that the spin time is additive to the syscall timeout, not inclusive.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: rui.zhang@intel.com
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/net/busy_poll.h')
-rw-r--r-- | include/net/busy_poll.h | 19 |
1 files changed, 1 insertions, 18 deletions
diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h index 829627d7b846..1d67fb6b23a0 100644 --- a/include/net/busy_poll.h +++ b/include/net/busy_poll.h @@ -42,27 +42,10 @@ static inline bool net_busy_loop_on(void) return sysctl_net_busy_poll; } -/* a wrapper to make debug_smp_processor_id() happy - * we can use sched_clock() because we don't care much about precision - * we only care that the average is bounded - */ -#ifdef CONFIG_DEBUG_PREEMPT -static inline u64 busy_loop_us_clock(void) -{ - u64 rc; - - preempt_disable_notrace(); - rc = sched_clock(); - preempt_enable_no_resched_notrace(); - - return rc >> 10; -} -#else /* CONFIG_DEBUG_PREEMPT */ static inline u64 busy_loop_us_clock(void) { - return sched_clock() >> 10; + return local_clock() >> 10; } -#endif /* CONFIG_DEBUG_PREEMPT */ static inline unsigned long sk_busy_loop_end_time(struct sock *sk) { |