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

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Date:   Thu, 27 Jan 2022 08:30:09 -0800
From:   Colin Foster <colin.foster@...advantage.com>
To:     Jakub Kicinski <kuba@...nel.org>
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

Hi Jakub,

On Wed, Jan 26, 2022 at 06:34:36PM -0800, Jakub Kicinski wrote:
> 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()

Good catch. I'll probably give it another day for review and resubmit 
tomrrow. 

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