linux-kernel - Re: [PATCH v2 1/4] drm/etnaviv: add simple moving average (SMA)

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Date:   Fri, 24 Jun 2022 11:22:39 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Christian Gmeiner <christian.gmeiner@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>,
        "moderated list:DRM DRIVERS FOR VIVANTE GPU IP" 
        <etnaviv@...ts.freedesktop.org>,
        "open list:DRM DRIVERS FOR VIVANTE GPU IP" 
        <dri-devel@...ts.freedesktop.org>, Daniel Vetter <daniel@...ll.ch>,
        Russell King <linux+etnaviv@...linux.org.uk>
Subject: Re: [PATCH v2 1/4] drm/etnaviv: add simple moving average (SMA)

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@...il.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__ */