Commit 6acc72a4 authored by Vladimir Oltean's avatar Vladimir Oltean Committed by Jakub Kicinski

net: mscc: ocelot: fix stats region batching

The blamed commit changed struct ocelot_stat_layout :: "u32 offset" to
"u32 reg".

However, "u32 reg" is not quite a register address, but an enum
ocelot_reg, which in itself encodes an enum ocelot_target target in the
upper bits, and an index into the ocelot->map[target][] array in the
lower bits.

So, whereas the previous code comparison between stats_layout[i].offset
and last + 1 was correct (because those "offsets" at the time were
32-bit relative addresses), the new code, comparing layout[i].reg to
last + 4 is not correct, because the "reg" here is an enum/index, not an
actual register address.

What we want to compare are indeed register addresses, but to do that,
we need to actually go through the same motions as
__ocelot_bulk_read_ix() itself.

With this bug, all statistics counters are deemed by
ocelot_prepare_stats_regions() as constituting their own region.
(Truncated) log on VSC9959 (Felix) below (prints added by me):

Before:

region of 1 contiguous counters starting with SYS:STAT:CNT[0x000]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x001]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x002]
...
region of 1 contiguous counters starting with SYS:STAT:CNT[0x041]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x042]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x080]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x081]
...
region of 1 contiguous counters starting with SYS:STAT:CNT[0x0ac]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x100]
region of 1 contiguous counters starting with SYS:STAT:CNT[0x101]
...
region of 1 contiguous counters starting with SYS:STAT:CNT[0x111]

After:

region of 67 contiguous counters starting with SYS:STAT:CNT[0x000]
region of 45 contiguous counters starting with SYS:STAT:CNT[0x080]
region of 18 contiguous counters starting with SYS:STAT:CNT[0x100]

Since commit d87b1c08 ("net: mscc: ocelot: use bulk reads for
stats") intended bulking as a performance improvement, and since now,
with trivial-sized regions, performance is even worse than without
bulking at all, this could easily qualify as a performance regression.

Fixes: d4c36765 ("net: mscc: ocelot: keep ocelot_stat_layout by reg address, not offset")
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: default avatarColin Foster <colin.foster@in-advantage.com>
Tested-by: default avatarColin Foster <colin.foster@in-advantage.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 8e50ed77
......@@ -899,7 +899,8 @@ static int ocelot_prepare_stats_regions(struct ocelot *ocelot)
if (!layout[i].reg)
continue;
if (region && layout[i].reg == last + 4) {
if (region && ocelot->map[SYS][layout[i].reg & REG_MASK] ==
ocelot->map[SYS][last & REG_MASK] + 4) {
region->count++;
} else {
region = devm_kzalloc(ocelot->dev, sizeof(*region),
......
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