Date:   Tue, 8 Feb 2022 13:18:50 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Colin Foster <colin.foster@...advantage.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>
Subject: Re: [PATCH v5 net-next 3/3] net: mscc: ocelot: use bulk reads for
 stats

On Mon, Feb 07, 2022 at 08:46:44PM -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>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@....com>

Just one minor comment below, but all in all it's fine as is, too.

>  drivers/net/ethernet/mscc/ocelot.c | 78 +++++++++++++++++++++++++-----
>  include/soc/mscc/ocelot.h          |  8 +++
>  2 files changed, 73 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index 455293aa6343..5efb1f3a1410 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -1737,32 +1737,41 @@ void ocelot_get_strings(struct ocelot *ocelot, int port, u32 sset, u8 *data)
>  }
>  EXPORT_SYMBOL(ocelot_get_strings);
>  
> -static void ocelot_update_stats(struct ocelot *ocelot)
> +static int ocelot_update_stats(struct ocelot *ocelot)
>  {
> -	int i, j;
> +	struct ocelot_stats_region *region;
> +	int i, j, err = 0;
>  
>  	mutex_lock(&ocelot->stats_lock);
>  
>  	for (i = 0; i < ocelot->num_phys_ports; i++) {
> +		unsigned int idx = 0;
> +
>  		/* Configure the port to read the stats from */
>  		ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(i), SYS_STAT_CFG);
>  
> -		for (j = 0; j < ocelot->num_stats; j++) {
> -			u32 val;
> -			unsigned int idx = i * ocelot->num_stats + j;
> +		list_for_each_entry(region, &ocelot->stats_regions, node) {
> +			err = ocelot_bulk_read_rix(ocelot, SYS_COUNT_RX_OCTETS,
> +						   region->offset, region->buf,
> +						   region->count);
> +			if (err)
> +				goto out;
>  
> -			val = ocelot_read_rix(ocelot, SYS_COUNT_RX_OCTETS,
> -					      ocelot->stats_layout[j].offset);
> +			for (j = 0; j < region->count; j++) {
> +				if (region->buf[j] < (ocelot->stats[idx + j] & U32_MAX))
> +					ocelot->stats[idx + j] += (u64)1 << 32;
>  
> -			if (val < (ocelot->stats[idx] & U32_MAX))
> -				ocelot->stats[idx] += (u64)1 << 32;
> +				ocelot->stats[idx + j] = (ocelot->stats[idx + j] &
> +							~(u64)U32_MAX) + region->buf[j];
> +			}
>  
> -			ocelot->stats[idx] = (ocelot->stats[idx] &
> -					      ~(u64)U32_MAX) + val;
> +			idx += region->count;
>  		}
>  	}
>  
> +out:
>  	mutex_unlock(&ocelot->stats_lock);
> +	return err;
>  }
>  
>  static void ocelot_check_stats_work(struct work_struct *work)
> @@ -1779,10 +1788,11 @@ static void ocelot_check_stats_work(struct work_struct *work)
>  
>  void ocelot_get_ethtool_stats(struct ocelot *ocelot, int port, u64 *data)
>  {
> -	int i;
> +	int i, err;
>  
>  	/* check and update now */
> -	ocelot_update_stats(ocelot);
> +	err = ocelot_update_stats(ocelot);
> +	WARN_ONCE(err, "Error %d updating ethtool stats\n", err);

I think a dev_err(ocelot->dev, ...) would be more appropriate here.
WARN_ON() should be used for truly critical errors (things that should
never happen unless bugs are present). When the assertion holds true, a
WARN_ON() will print a stack trace, and when "panic_on_warn" is enabled,
a WARN() is effectively a BUG() and crashes the kernel.

include/asm-generic/bug.h says:

/*
 * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
 * significant kernel issues that need prompt attention if they should ever
 * appear at runtime.
 *
 * Do not use these macros when checking for invalid external inputs
 * (e.g. invalid system call arguments, or invalid data coming from
 * network/devices), and on transient conditions like ENOMEM or EAGAIN.
 * These macros should be used for recoverable kernel issues only.
 * For invalid external inputs, transient conditions, etc use
 * pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary.
 * Do not include "BUG"/"WARNING" in format strings manually to make these
 * conditions distinguishable from kernel issues.
 *
 * Use the versions with printk format strings to provide better diagnostics.
 */

>  
>  	/* Copy all counters */
>  	for (i = 0; i < ocelot->num_stats; i++)
> @@ -1799,6 +1809,41 @@ int ocelot_get_sset_count(struct ocelot *ocelot, int port, int sset)
>  }
>  EXPORT_SYMBOL(ocelot_get_sset_count);
>  
> +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_kcalloc(ocelot->dev, region->count,
> +					   sizeof(*region->buf), GFP_KERNEL);
> +		if (!region->buf)
> +			return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
>  int ocelot_get_ts_info(struct ocelot *ocelot, int port,
>  		       struct ethtool_ts_info *info)
>  {
> @@ -2799,6 +2844,13 @@ int ocelot_init(struct ocelot *ocelot)
>  				 ANA_CPUQ_8021_CFG_CPUQ_BPDU_VAL(6),
>  				 ANA_CPUQ_8021_CFG, i);
>  
> +	ret = ocelot_prepare_stats_regions(ocelot);
> +	if (ret) {
> +		destroy_workqueue(ocelot->stats_queue);
> +		destroy_workqueue(ocelot->owq);
> +		return ret;
> +	}
> +
>  	INIT_DELAYED_WORK(&ocelot->stats_work, ocelot_check_stats_work);
>  	queue_delayed_work(ocelot->stats_queue, &ocelot->stats_work,
>  			   OCELOT_STATS_CHECK_DELAY);
> diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
> index 312b72558659..d3291a5f7e88 100644
> --- a/include/soc/mscc/ocelot.h
> +++ b/include/soc/mscc/ocelot.h
> @@ -542,6 +542,13 @@ struct ocelot_stat_layout {
>  	char name[ETH_GSTRING_LEN];
>  };
>  
> +struct ocelot_stats_region {
> +	struct list_head node;
> +	u32 offset;
> +	int count;
> +	u32 *buf;
> +};
> +
>  enum ocelot_tag_prefix {
>  	OCELOT_TAG_PREFIX_DISABLED	= 0,
>  	OCELOT_TAG_PREFIX_NONE,
> @@ -673,6 +680,7 @@ struct ocelot {
>  	struct regmap_field		*regfields[REGFIELD_MAX];
>  	const u32 *const		*map;
>  	const struct ocelot_stat_layout	*stats_layout;
> +	struct list_head		stats_regions;
>  	unsigned int			num_stats;
>  
>  	u32				pool_size[OCELOT_SB_NUM][OCELOT_SB_POOL_NUM];
> -- 
> 2.25.1
>

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