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SubjectRe: [PATCH v2 1/4] drm/etnaviv: add simple moving average (SMA)
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Hi Christian,

Am Dienstag, dem 21.06.2022 um 09:20 +0200 schrieb Christian Gmeiner:
> This adds a SMA algorithm inspired by Exponentially weighted moving
> average (EWMA) algorithm found in the kernel.
>
Still not sure about this one. I _feel_ that a simple moving average
over a period of one second does not do a good job of reflecting the
real GPU load for a bursty workload, where EWMA might be better suited.
But then I also don't have a real informed opinion to offer on this.

Regards,
Lucas

> Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
> ---
> drivers/gpu/drm/etnaviv/etnaviv_sma.h | 53 +++++++++++++++++++++++++++
> 1 file changed, 53 insertions(+)
> create mode 100644 drivers/gpu/drm/etnaviv/etnaviv_sma.h
>
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sma.h b/drivers/gpu/drm/etnaviv/etnaviv_sma.h
> new file mode 100644
> index 000000000000..81564d5cbdc3
> --- /dev/null
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_sma.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020 Etnaviv Project
> + */
> +
> +#ifndef __ETNAVIV_SMA_H__
> +#define __ETNAVIV_SMA_H__
> +
> +#include <linux/bug.h>
> +#include <linux/compiler.h>
> +
> +/*
> + * Simple moving average (SMA)
> + *
> + * This implements a fixed-size SMA algorithm.
> + *
> + * The first argument to the macro is the name that will be used
> + * for the struct and helper functions.
> + *
> + * The second argument, the samples, expresses how many samples are
> + * used for the SMA algorithm.
> + */
> +
> +#define DECLARE_SMA(name, _samples) \
> + struct sma_##name { \
> + unsigned long pos; \
> + unsigned long sum; \
> + unsigned long samples[_samples]; \
> + }; \
> + static inline void sma_##name##_init(struct sma_##name *s) \
> + { \
> + BUILD_BUG_ON(!__builtin_constant_p(_samples)); \
> + memset(s, 0, sizeof(struct sma_##name)); \
> + } \
> + static inline unsigned long sma_##name##_read(struct sma_##name *s) \
> + { \
> + BUILD_BUG_ON(!__builtin_constant_p(_samples)); \
> + return s->sum / _samples; \
> + } \
> + static inline void sma_##name##_add(struct sma_##name *s, unsigned long val) \
> + { \
> + unsigned long pos = READ_ONCE(s->pos); \
> + unsigned long sum = READ_ONCE(s->sum); \
> + unsigned long sample = READ_ONCE(s->samples[pos]); \
> + \
> + BUILD_BUG_ON(!__builtin_constant_p(_samples)); \
> + \
> + WRITE_ONCE(s->sum, sum - sample + val); \
> + WRITE_ONCE(s->samples[pos], val); \
> + WRITE_ONCE(s->pos, pos + 1 == _samples ? 0 : pos + 1); \
> + }
> +
> +#endif /* __ETNAVIV_SMA_H__ */


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