Subject: Re: [PATCH v6 net-next 5/5] net: mscc: ocelot: use bulk reads for stats

From: Colin Foster <[email-masked]>
Date: Thu, 10 Feb 2022 07:21:03 -0800

On Thu, Feb 10, 2022 at 10:36:37AM +0000, Vladimir Oltean wrote:
> On Wed, Feb 09, 2022 at 08:13:45PM -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 <[email-masked]>
> > ---
> >  drivers/net/ethernet/mscc/ocelot.c | 79 +++++++++++++++++++++++++-----
> >  include/soc/mscc/ocelot.h          |  8 +++
> >  2 files changed, 75 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> > index ab36732e7d3f..fdbd31149dfc 100644
> > --- a/drivers/net/ethernet/mscc/ocelot.c
> > +++ b/drivers/net/ethernet/mscc/ocelot.c
> > @@ -1738,25 +1738,36 @@ void ocelot_get_strings(struct ocelot *ocelot, int port, u32 sset, u8 *data)
> >  EXPORT_SYMBOL(ocelot_get_strings);
> >  
> >  /* Caller must hold &ocelot->stats_lock */
> > -static void ocelot_update_stats_for_port(struct ocelot *ocelot, int port)
> > +static int ocelot_update_stats_for_port(struct ocelot *ocelot, int port)
> >  {
> > -	int j;
> > +	unsigned int idx = port * ocelot->num_stats;
> > +	struct ocelot_stats_region *region;
> > +	int err, j;
> >  
> >  	/* Configure the port to read the stats from */
> >  	ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(port), SYS_STAT_CFG);
> >  
> > -	for (j = 0; j < ocelot->num_stats; j++) {
> > -		u32 val;
> > -		unsigned int idx = port * 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)
> > +			return err;
> >  
> > -		val = ocelot_read_rix(ocelot, SYS_COUNT_RX_OCTETS,
> > -				      ocelot->stats_layout[j].offset);
> > +		for (j = 0; j < region->count; j++) {
> > +			u64 *stat = &ocelot->stats[idx + j];
> > +			u64 val = region->buf[j];
> >  
> > -		if (val < (ocelot->stats[idx] & U32_MAX))
> > -			ocelot->stats[idx] += (u64)1 << 32;
> > +			if (val < (*stat & U32_MAX))
> > +				*stat += (u64)1 << 32;
> > +
> > +			*stat = (*stat & ~(u64)U32_MAX) + val;
> > +		}
> >  
> > -		ocelot->stats[idx] = (ocelot->stats[idx] & ~(u64)U32_MAX) + val;
> > +		idx += region->count;
> >  	}
> > +
> > +	return err;
> >  }
> >  
> >  static void ocelot_check_stats_work(struct work_struct *work)
> > @@ -1777,12 +1788,14 @@ 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;
> >  
> >  	mutex_lock(&ocelot->stats_lock);
> >  
> >  	/* check and update now */
> > -	ocelot_update_stats_for_port(ocelot, port);
> > +	err = ocelot_update_stats_for_port(ocelot, port);
> 
> ocelot_check_stats_work() should also check for errors.

Another change I'm catching: I assume calling dev_err while holding a
mutex is frowned upon, so I'm moving this err check after the counter
copy / mutex unlock. I'll submit that fix after patch 1 gets merged into
net / mainline.

> 
> > +	if (err)
> > +		dev_err(ocelot->dev, "Error %d updating ethtool stats\n", err);
> >  
> >  	/* Copy all counters */
> >  	for (i = 0; i < ocelot->num_stats; i++)
> > @@ -1801,6 +1814,41 @@ 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)
> >  {
> > @@ -2801,6 +2849,13 @@ 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
> >