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Message-ID: <1486660204.7793.104.camel@edumazet-glaptop3.roam.corp.google.com>
Date: Thu, 09 Feb 2017 09:10:04 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Tariq Toukan <tariqt@...lanox.com>,
Shawn Bohrer <sbohrer@...advisors.com>
Subject: [PATCH net-next] mlx4: do not use rwlock in fast path
From: Eric Dumazet <edumazet@...gle.com>
Using a reader-writer lock in fast path is silly, when we can
instead use RCU or a seqlock.
For mlx4 hwstamp clock, a seqlock is the way to go, removing
two atomic operations and false sharing.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Tariq Toukan <tariqt@...lanox.com>
---
drivers/net/ethernet/mellanox/mlx4/en_clock.c | 35 ++++++++--------
drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 2
2 files changed, 19 insertions(+), 18 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
index 504461a464c581bf77b5cca127680f262222..e7b81a305469e64b97f68bc0e2bcb064b78f 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
@@ -62,12 +62,13 @@ void mlx4_en_fill_hwtstamps(struct mlx4_en_dev *mdev,
struct skb_shared_hwtstamps *hwts,
u64 timestamp)
{
- unsigned long flags;
+ unsigned int seq;
u64 nsec;
- read_lock_irqsave(&mdev->clock_lock, flags);
- nsec = timecounter_cyc2time(&mdev->clock, timestamp);
- read_unlock_irqrestore(&mdev->clock_lock, flags);
+ do {
+ seq = read_seqbegin(&mdev->clock_lock);
+ nsec = timecounter_cyc2time(&mdev->clock, timestamp);
+ } while (read_seqretry(&mdev->clock_lock, seq));
memset(hwts, 0, sizeof(struct skb_shared_hwtstamps));
hwts->hwtstamp = ns_to_ktime(nsec);
@@ -95,9 +96,9 @@ void mlx4_en_ptp_overflow_check(struct mlx4_en_dev *mdev)
unsigned long flags;
if (timeout) {
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
timecounter_read(&mdev->clock);
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
mdev->last_overflow_check = jiffies;
}
}
@@ -128,10 +129,10 @@ static int mlx4_en_phc_adjfreq(struct ptp_clock_info *ptp, s32 delta)
adj *= delta;
diff = div_u64(adj, 1000000000ULL);
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
timecounter_read(&mdev->clock);
mdev->cycles.mult = neg_adj ? mult - diff : mult + diff;
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
return 0;
}
@@ -149,9 +150,9 @@ static int mlx4_en_phc_adjtime(struct ptp_clock_info *ptp, s64 delta)
ptp_clock_info);
unsigned long flags;
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
timecounter_adjtime(&mdev->clock, delta);
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
return 0;
}
@@ -172,9 +173,9 @@ static int mlx4_en_phc_gettime(struct ptp_clock_info *ptp,
unsigned long flags;
u64 ns;
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
ns = timecounter_read(&mdev->clock);
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
*ts = ns_to_timespec64(ns);
@@ -198,9 +199,9 @@ static int mlx4_en_phc_settime(struct ptp_clock_info *ptp,
unsigned long flags;
/* reset the timecounter */
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
timecounter_init(&mdev->clock, &mdev->cycles, ns);
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
return 0;
}
@@ -266,7 +267,7 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
if (mdev->ptp_clock)
return;
- rwlock_init(&mdev->clock_lock);
+ seqlock_init(&mdev->clock_lock);
memset(&mdev->cycles, 0, sizeof(mdev->cycles));
mdev->cycles.read = mlx4_en_read_clock;
@@ -276,10 +277,10 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
clocksource_khz2mult(1000 * dev->caps.hca_core_clock, mdev->cycles.shift);
mdev->nominal_c_mult = mdev->cycles.mult;
- write_lock_irqsave(&mdev->clock_lock, flags);
+ write_seqlock_irqsave(&mdev->clock_lock, flags);
timecounter_init(&mdev->clock, &mdev->cycles,
ktime_to_ns(ktime_get_real()));
- write_unlock_irqrestore(&mdev->clock_lock, flags);
+ write_sequnlock_irqrestore(&mdev->clock_lock, flags);
/* Calculate period in seconds to call the overflow watchdog - to make
* sure counter is checked at least once every wrap around.
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index 52f157cea7765ad6907c59aead357a158848..59f67cdd27d65125138c746fbb615d945d53 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -417,9 +417,9 @@ struct mlx4_en_dev {
u32 priv_pdn;
spinlock_t uar_lock;
u8 mac_removed[MLX4_MAX_PORTS + 1];
- rwlock_t clock_lock;
u32 nominal_c_mult;
struct cyclecounter cycles;
+ seqlock_t clock_lock;
struct timecounter clock;
unsigned long last_overflow_check;
unsigned long overflow_period;
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