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MINOR: freq_ctr: Make the sliding window sums thread-safe 

swrate_add() and swrate_add_scaled() now rely on the CAS atomic operation. So
the sliding window sums are atomically updated.
This commit is contained in:
Christopher Faulet 2019-11-08 14:40:18 +01:00
parent b2e58492b1
commit e2e8c6779e
1 changed files with 18 additions and 4 deletions
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22
include/proto/freq_ctr.h
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@ -248,11 +248,18 @@ unsigned int freq_ctr_remain_period(struct freq_ctr_period *ctr, unsigned int pe
*/ */
/* Adds sample value <v> to sliding window sum <sum> configured for <n> samples. /* Adds sample value <v> to sliding window sum <sum> configured for <n> samples.
* The sample is returned. Better if <n> is a power of two. * The sample is returned. Better if <n> is a power of two. This function is
* thread-safe.
*/ */
static inline unsigned int swrate_add(unsigned int *sum, unsigned int n, unsigned int v) static inline unsigned int swrate_add(unsigned int *sum, unsigned int n, unsigned int v)
{ {
return *sum = *sum - (*sum + n - 1) / n + v; unsigned int new_sum, old_sum;
old_sum = *sum;
do {
new_sum = old_sum - (old_sum + n - 1) / n + v;
} while (!_HA_ATOMIC_CAS(sum, &old_sum, new_sum));
return new_sum;
} }
/* Adds sample value <v> spanning <s> samples to sliding window sum <sum> /* Adds sample value <v> spanning <s> samples to sliding window sum <sum>
@ -275,11 +282,18 @@ static inline unsigned int swrate_add(unsigned int *sum, unsigned int n, unsigne
* Thus the simplified function effectively replaces a part of the history with * Thus the simplified function effectively replaces a part of the history with
* a linear sum instead of applying the exponential one. But as long as s/n is * a linear sum instead of applying the exponential one. But as long as s/n is
* "small enough", the error fades away and remains small for both small and * "small enough", the error fades away and remains small for both small and
* large values of n and s (typically < 0.2% measured). * large values of n and s (typically < 0.2% measured). This function is
* thread-safe.
*/ */
static inline unsigned int swrate_add_scaled(unsigned int *sum, unsigned int n, unsigned int v, unsigned int s) static inline unsigned int swrate_add_scaled(unsigned int *sum, unsigned int n, unsigned int v, unsigned int s)
{ {
return *sum = *sum + v * s - div64_32((unsigned long long)(*sum + n) * s, n); unsigned int new_sum, old_sum;
old_sum = *sum;
do {
new_sum = old_sum + v * s - div64_32((unsigned long long)(old_sum + n) * s, n);
} while (!_HA_ATOMIC_CAS(sum, &old_sum, new_sum));
return new_sum;
} }
/* Returns the average sample value for the sum <sum> over a sliding window of /* Returns the average sample value for the sum <sum> over a sliding window of