[PATCH net] octeontx2-pf: tc: fix egress ratelimiting
From: <hidden>
Date: 2026-07-17 08:44:19
Also in:
lkml
Subsystem:
marvell octeontx2 physical function driver, networking drivers, the rest · Maintainers:
Sunil Goutham, Geetha sowjanya, Ratheesh Kannoth, Subbaraya Sundeep, Bharat Bhushan, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Hariprasad Kelam <redacted>
The egress rate calculation computes an incorrect mantissa and exponent,
causing up to ~50% deviation from the configured rate at lower speeds.
Rework the computation to follow the hardware rate formula:
rate = 2 * (1 + mantissa/256) * 2^exp / (1 << div_exp)
Keep div_exp = 0 and derive exp and mantissa from half of the requested
rate. Rates below 2 Mbps are floored to the smallest encodable step
(exp = 0, mantissa = 0).
Fixes: e638a83f167e ("octeontx2-pf: TC_MATCHALL egress ratelimiting offload")
Signed-off-by: Hariprasad Kelam <redacted>
Signed-off-by: Nitin Shetty J <redacted>
---
.../ethernet/marvell/octeontx2/nic/otx2_tc.c | 29 ++++++++++---------
1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c
index 40162b08014d..0b46ec29e64e 100644
--- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c
+++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_tc.c@@ -30,6 +30,7 @@ #define OTX2_UNSUPP_LSE_DEPTH GENMASK(6, 4) #define MCAST_INVALID_GRP (-1U) +#define RATE_MANTISSA_BITS 8 static void otx2_get_egress_burst_cfg(struct otx2_nic *nic, u32 burst, u32 *burst_exp, u32 *burst_mantissa)
@@ -66,28 +67,30 @@ static void otx2_get_egress_burst_cfg(struct otx2_nic *nic, u32 burst, static void otx2_get_egress_rate_cfg(u64 maxrate, u32 *exp, u32 *mantissa, u32 *div_exp) { - u64 tmp; - /* Rate calculation by hardware * * PIR_ADD = ((256 + mantissa) << exp) / 256 * rate = (2 * PIR_ADD) / ( 1 << div_exp) * The resultant rate is in Mbps. + * + * Use div_exp = 0 and compute exp/mantissa for maxrate / 2; the + * leading factor of two yields the full rate. Rates below 2 Mbps + * are floored to the smallest step (exp = 0, mantissa = 0). */ - /* 2Mbps to 100Gbps can be expressed with div_exp = 0. - * Setting this to '0' will ease the calculation of - * exponent and mantissa. - */ *div_exp = 0; - if (maxrate) { - *exp = ilog2(maxrate) ? ilog2(maxrate) - 1 : 0; - tmp = maxrate - rounddown_pow_of_two(maxrate); - if (maxrate < MAX_RATE_MANTISSA) - *mantissa = tmp * 2; - else - *mantissa = tmp / (1ULL << (*exp - 7)); + maxrate = maxrate / 2; + if (!maxrate) { + /* Rates below 2 Mbps map to the smallest step */ + *exp = 0; + *mantissa = 0; + } else { + *exp = ilog2(maxrate); + /* Clear MSB and derive fractional bits */ + maxrate &= ~BIT(*exp); + *mantissa = (maxrate << RATE_MANTISSA_BITS) >> *exp; + } } else { /* Instead of disabling rate limiting, set all values to max */ *exp = MAX_RATE_EXPONENT;
--
2.48.1