This is a note to let you know that I've just added the patch titled
net: mscc: ocelot: fix stats region batching
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-mscc-ocelot-fix-stats-region-batching.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1bfdf14cb0563cc7e444a87f59d86d4977edc782
Author: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Date: Tue Mar 21 03:03:23 2023 +0200
net: mscc: ocelot: fix stats region batching
[ Upstream commit 6acc72a43eac78a309160d0a7512bbc59bcdd757 ]
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 d87b1c08f38a ("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: d4c367650704 ("net: mscc: ocelot: keep ocelot_stat_layout by reg address, not offset")
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Acked-by: Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>
Tested-by: Colin Foster <colin.foster@xxxxxxxxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/net/ethernet/mscc/ocelot_stats.c b/drivers/net/ethernet/mscc/ocelot_stats.c
index dbd20b125ceaf..0066219bb0e89 100644
--- a/drivers/net/ethernet/mscc/ocelot_stats.c
+++ b/drivers/net/ethernet/mscc/ocelot_stats.c
@@ -392,7 +392,8 @@ static int ocelot_prepare_stats_regions(struct ocelot *ocelot)
if (!ocelot->stats_layout[i].reg)
continue;
- if (region && ocelot->stats_layout[i].reg == last + 4) {
+ if (region && ocelot->map[SYS][ocelot->stats_layout[i].reg & REG_MASK] ==
+ ocelot->map[SYS][last & REG_MASK] + 4) {
region->count++;
} else {
region = devm_kzalloc(ocelot->dev, sizeof(*region),
