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: Vladimir Oltean <vladimir.oltean@nxp.com> Acked-by: Colin Foster <colin.foster@in-advantage.com> Tested-by: Colin Foster <colin.foster@in-advantage.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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