Commit 5d867836 authored Dec 03, 2018 by Miroslav Lichvar Committed by Saeed Mahameed Dec 20, 2018

mlx5: update timecounter at least twice per counter overflow



The timecounter needs to be updated at least once in half of the
cyclecounter interval to prevent timecounter_cyc2time() interpreting a
new timestamp as an old value and causing a backward jump.

This would be an issue if the timecounter multiplier was so small that
the update interval would not be limited by the 64-bit overflow in
multiplication.

Shorten the calculated interval to make sure the timecounter is updated
in time even when the system clock is slowed down by up to 10%, the
multiplier is increased by up to 10%, and the scheduled overflow check
is late by 15%.

Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Ariel Levkovich <lariel@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

parent a9cd3439

drivers/net/ethernet/mellanox/mlx5/core/lib/clock.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -517,14 +517,14 @@ void mlx5_init_clock(struct mlx5_core_dev *mdev)
		ktime_to_ns(ktime_get_real()));

		/* Calculate period in seconds to call the overflow watchdog - to make
		* sure counter is checked at least once every wrap around.
		* sure counter is checked at least twice every wrap around.
		* The period is calculated as the minimum between max HW cycles count
		* (The clock source mask) and max amount of cycles that can be
		* multiplied by clock multiplier where the result doesn't exceed
		* 64bits.
		*/
		overflow_cycles = div64_u64(~0ULL >> 1, clock->cycles.mult);
		overflow_cycles = min(overflow_cycles, clock->cycles.mask >> 1);
		overflow_cycles = min(overflow_cycles, div_u64(clock->cycles.mask, 3));

		ns = cyclecounter_cyc2ns(&clock->cycles, overflow_cycles,
		frac, &frac);

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