Re: [PATCH v5 net-next 3/3] net: mscc: ocelot: use bulk reads for stats

Colin Foster
2022-02-08T15:42:08Z

Hi Vladimir,

On Tue, Feb 08, 2022 at 03:03:04PM +0000, Vladimir Oltean wrote:
> 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@in-advantage.com>
> > ---
> > 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;
> > +
>
> This is a bug which causes ocelot->stats to be overwritten with the
> statistics of port 0, for all ports. Either move the variable
> declaration and initialization with 0 in the larger scope (outside the
> "for" loop), or initialize idx with i * ocelot->num_stats.

I see that now. It is confusing and I'll clear it up. I never caught
this because I'm testing in a setup where port 0 is the CPU port, so I
can't get ethtool stats. Thanks!

>
> > /* 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;
>
> I'd prefer if you reduce the apparent complexity of this logic by
> creating some temporary variables:
>
> u64 *stat = &ocelot->stats[idx + j];
> u64 val = region->buf[j];

Can do. Thanks for the suggestion.

>
> >
> > - 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);
>
> Please, as a separate change, introduce a function that reads the
> statistics for a single port, and make ethtool call that and not the
> entire port array, it's pointless.
>
> > + WARN_ONCE(err, "Error %d updating ethtool stats\n", err);
> >
> > /* Copy all counters */
> > for (i = 0; i < ocelot->num_stats; i++)
>
> and here, in the unseen part of the context, lies:
>
> /* Copy all counters */
> for (i = 0; i < ocelot->num_stats; i++)
> *data++ = ocelot->stats[port * ocelot->num_stats + i];
>
> I think this is buggy, because this is a reader of ocelot->stats which
> is not protected by ocelot->stats_lock (it was taken and dropped by
> ocelot_update_stats). But a second ocelot_update_stats() can run
> concurrently with ethtool and ruin the day, modifying the array at the
> same time as it's being read out.
>
> The new function that you introduce, for reading the stats of a single
> port, should require that ocelot->stats_lock is already held, and you
> should hold it from top-level (ocelot_get_ethtool_stats).

I'll add this fix as a separate patch. Thanks as always for the
feedback!

>
> > @@ -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
> >