netdev - Re: [PATCH v3 net-next 2/2] net: mscc: ocelot: use bulk reads for stats

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Date:   Wed, 26 Jan 2022 18:34:36 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Colin Foster <colin.foster@...advantage.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        UNGLinuxDriver@...rochip.com,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH v3 net-next 2/2] net: mscc: ocelot: use bulk reads for
 stats

On Mon, 24 Jan 2022 23:15:31 -0800 Colin Foster wrote:
> Create and utilize bulk regmap reads instead of single access for gathering
> stats. The background reading of statistics happens frequently, and over
> a few contiguous memory regions.
> 
> High speed PCIe buses and MMIO access will probably see negligible
> performance increase. Lower speed buses like SPI and I2C could see
> significant performance increase, since the bus configuration and register
> access times account for a large percentage of data transfer time.
> 
> Signed-off-by: Colin Foster <colin.foster@...advantage.com>

> +static int ocelot_prepare_stats_regions(struct ocelot *ocelot)
> +{
> +	struct ocelot_stats_region *region = NULL;
> +	unsigned int last;
> +	int i;
> +
> +	INIT_LIST_HEAD(&ocelot->stats_regions);
> +
> +	for (i = 0; i < ocelot->num_stats; i++) {
> +		if (region && ocelot->stats_layout[i].offset == last + 1) {
> +			region->count++;
> +		} else {
> +			region = devm_kzalloc(ocelot->dev, sizeof(*region),
> +					      GFP_KERNEL);
> +			if (!region)
> +				return -ENOMEM;
> +
> +			region->offset = ocelot->stats_layout[i].offset;
> +			region->count = 1;
> +			list_add_tail(&region->node, &ocelot->stats_regions);
> +		}
> +
> +		last = ocelot->stats_layout[i].offset;
> +	}
> +
> +	list_for_each_entry(region, &ocelot->stats_regions, node) {
> +		region->buf = devm_kzalloc(ocelot->dev,
> +					   region->count * sizeof(*region->buf),
> +					   GFP_KERNEL);

devm_kcalloc()

> +

unnecessary new line

> +		if (!region->buf)
> +			return -ENOMEM;