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authorTobias Klauser <tklauser@distanz.ch>2013-07-13 14:46:21 +0200
committerTobias Klauser <tklauser@distanz.ch>2013-07-13 14:46:21 +0200
commit22ed65468335a3d803b74db2d4ee39344a4543cc (patch)
tree856fa337b11d2d1f4d40e303a1574f92f8e84f14 /curve.h
parentdd123b0fb6af4909aa30940a8dc34661e8b1c420 (diff)
ifpps: Correct calculation of median values for CPU load
ifpps always reported the same values for median as for average in the CPU load fields (usr, sys, idle, iowait). This is of course incorrect. The bug was due to 3 sub-problems: - Summing up long double values (m_cpu_*) in an uint64_t (all) - Not using %Lf (for long double) in mvwprintw() - Explicitely use floating point division in MEDIAN_EVEN Fix the bug by summing up in a separate accumulator of type long double, use the correct format string for long double and divide by 2.0 in MEDIAN_EVEN to force the result to be (long) double. Reported-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
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llection of this here problem. Aside from the intermediate value hitting memory and causing problems, there's another problem: the underflow detection relies on the signed bit. This reduces the effective width of the variables, IOW its effectively the same as having these variables be of signed type. This patch changes to a different means of unsigned underflow detection to not rely on the signed bit. This allows the variables to use the 'full' unsigned range. And it does so with explicit LOAD - STORE to ensure any intermediate value will never be visible in memory, allowing these unserialized loads. Note: GCC generates crap code for this, might warrant a look later. Note2: I say 'full' above, if we end up at U*_MAX we'll still explode; maybe we should do clamping on add too. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yuyang Du <yuyang.du@intel.com> Cc: bsegall@google.com Cc: kernel@kyup.com Cc: morten.rasmussen@arm.com Cc: pjt@google.com Cc: steve.muckle@linaro.org Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking") Link: http://lkml.kernel.org/r/20160617091948.GJ30927@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
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