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Date: Thu, 26 Dec 2013 16:41:11 +0200
From: Hadar Hen-Zion <hadarh@....mellanox.co.il>
To: Richard Cochran <richardcochran@...il.com>
Cc: Shawn Bohrer <shawn.bohrer@...il.com>,
Tom Ketterhagen <tomk@...advisors.com>,
netdev <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>,
Or Gerlitz <ogerlitz@...lanox.com>,
Hadar Hen Zion <hadarh@...lanox.com>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/2] mlx4_en: Add PTP hardware clock
On Thu, Dec 26, 2013 at 10:17:41AM +0100, Richard Cochran wrote:
> On Thu, Dec 26, 2013 at 10:33:26AM +0200, Hadar Hen Zion wrote:
> >
> > Is there a way to time stamping packets per socket?
>
> No, it is at the device level. Some devices support time stamping
> different types of packets, like PTP events.
>
> I looked again at your driver, and now it makes sense to me that the
> spin lock is so costly in your tests. Every received packet calls
> timecounter_cyc2time. So you will need locking, and I think
> reader/writer is perfectly fine for you to use.
>
> Thanks,
> Richard
> --
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The below patch is my suggestion for using RCU.
According to my test there is no performace loss with RCU.
If reader/writer is deprecated, why not using RCU?
Thanks,
Hadar
---
drivers/net/ethernet/mellanox/mlx4/en_clock.c | 82 +++++++++++++++---------
drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 2 +-
2 files changed, 52 insertions(+), 32 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
index cc6a546..2fbe9aa 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
@@ -107,17 +107,54 @@ void mlx4_en_fill_hwtstamps(struct mlx4_en_dev *mdev,
struct skb_shared_hwtstamps *hwts,
u64 timestamp)
{
- unsigned long flags;
u64 nsec;
- spin_lock_irqsave(&mdev->clock_lock, flags);
- nsec = timecounter_cyc2time(&mdev->clock, timestamp);
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ rcu_read_lock();
+ nsec = timecounter_cyc2time(rcu_dereference(mdev->clock), timestamp);
+ rcu_read_unlock();
memset(hwts, 0, sizeof(struct skb_shared_hwtstamps));
hwts->hwtstamp = ns_to_ktime(nsec);
}
+void mlx4_en_timecounter_init(struct mlx4_en_dev *mdev,
+ u64 start_tstamp)
+{
+ struct timecounter *new_tc, *old_tc;
+ unsigned long flags;
+
+ new_tc = kmalloc(sizeof(*new_tc), GFP_KERNEL);
+
+ spin_lock_irqsave(&mdev->clock_lock, flags);
+ old_tc = mdev->clock;
+ *new_tc = *old_tc;
+ timecounter_init(new_tc, &mdev->cycles, start_tstamp);
+ rcu_assign_pointer(mdev->clock, new_tc);
+ spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ synchronize_rcu();
+ kfree(old_tc);
+}
+
+u64 mlx4_en_timecounter_read(struct mlx4_en_dev *mdev)
+{
+ struct timecounter *new_tc, *old_tc;
+ unsigned long flags;
+ s64 now;
+
+ new_tc = kmalloc(sizeof(*new_tc), GFP_KERNEL);
+
+ spin_lock_irqsave(&mdev->clock_lock, flags);
+ old_tc = mdev->clock;
+ *new_tc = *old_tc;
+ now = timecounter_read(new_tc);
+ rcu_assign_pointer(mdev->clock, new_tc);
+ spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ synchronize_rcu();
+ kfree(old_tc);
+
+ return now;
+}
+
/**
* mlx4_en_remove_timestamp - disable PTP device
* @mdev: board private structure
@@ -129,6 +166,7 @@ void mlx4_en_remove_timestamp(struct mlx4_en_dev *mdev)
if (mdev->ptp_clock) {
ptp_clock_unregister(mdev->ptp_clock);
mdev->ptp_clock = NULL;
+ kfree(mdev->clock);
mlx4_info(mdev, "removed PHC\n");
}
}
@@ -137,12 +175,9 @@ void mlx4_en_ptp_overflow_check(struct mlx4_en_dev *mdev)
{
bool timeout = time_is_before_jiffies(mdev->last_overflow_check +
mdev->overflow_period);
- unsigned long flags;
if (timeout) {
- spin_lock_irqsave(&mdev->clock_lock, flags);
- timecounter_read(&mdev->clock);
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ mlx4_en_timecounter_read(mdev);
mdev->last_overflow_check = jiffies;
}
}
@@ -160,7 +195,6 @@ static int mlx4_en_phc_adjfreq(struct ptp_clock_info *ptp, s32 delta)
u64 adj;
u32 diff, mult;
int neg_adj = 0;
- unsigned long flags;
struct mlx4_en_dev *mdev = container_of(ptp, struct mlx4_en_dev,
ptp_clock_info);
@@ -173,10 +207,8 @@ static int mlx4_en_phc_adjfreq(struct ptp_clock_info *ptp, s32 delta)
adj *= delta;
diff = div_u64(adj, 1000000000ULL);
- spin_lock_irqsave(&mdev->clock_lock, flags);
- timecounter_read(&mdev->clock);
+ mlx4_en_timecounter_read(mdev);
mdev->cycles.mult = neg_adj ? mult - diff : mult + diff;
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
return 0;
}
@@ -192,14 +224,11 @@ static int mlx4_en_phc_adjtime(struct ptp_clock_info *ptp, s64 delta)
{
struct mlx4_en_dev *mdev = container_of(ptp, struct mlx4_en_dev,
ptp_clock_info);
- unsigned long flags;
s64 now;
- spin_lock_irqsave(&mdev->clock_lock, flags);
- now = timecounter_read(&mdev->clock);
+ now = mlx4_en_timecounter_read(mdev);
now += delta;
- timecounter_init(&mdev->clock, &mdev->cycles, now);
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ mlx4_en_timecounter_init(mdev, now);
return 0;
}
@@ -216,14 +245,10 @@ static int mlx4_en_phc_gettime(struct ptp_clock_info *ptp, struct timespec *ts)
{
struct mlx4_en_dev *mdev = container_of(ptp, struct mlx4_en_dev,
ptp_clock_info);
- unsigned long flags;
u32 remainder;
u64 ns;
- spin_lock_irqsave(&mdev->clock_lock, flags);
- ns = timecounter_read(&mdev->clock);
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
-
+ ns = mlx4_en_timecounter_read(mdev);
ts->tv_sec = div_u64_rem(ns, NSEC_PER_SEC, &remainder);
ts->tv_nsec = remainder;
@@ -244,12 +269,9 @@ static int mlx4_en_phc_settime(struct ptp_clock_info *ptp,
struct mlx4_en_dev *mdev = container_of(ptp, struct mlx4_en_dev,
ptp_clock_info);
u64 ns = timespec_to_ns(ts);
- unsigned long flags;
/* reset the timecounter */
- spin_lock_irqsave(&mdev->clock_lock, flags);
- timecounter_init(&mdev->clock, &mdev->cycles, ns);
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ mlx4_en_timecounter_init(mdev, ns);
return 0;
}
@@ -287,9 +309,9 @@ static const struct ptp_clock_info mlx4_en_ptp_clock_info = {
void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
{
struct mlx4_dev *dev = mdev->dev;
- unsigned long flags;
u64 ns;
+ mdev->clock = kmalloc(sizeof(struct timecounter), GFP_KERNEL);
memset(&mdev->cycles, 0, sizeof(mdev->cycles));
mdev->cycles.read = mlx4_en_read_clock;
mdev->cycles.mask = CLOCKSOURCE_MASK(48);
@@ -303,10 +325,7 @@ 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;
- spin_lock_irqsave(&mdev->clock_lock, flags);
- timecounter_init(&mdev->clock, &mdev->cycles,
- ktime_to_ns(ktime_get_real()));
- spin_unlock_irqrestore(&mdev->clock_lock, flags);
+ mlx4_en_timecounter_init(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.
@@ -323,6 +342,7 @@ void mlx4_en_init_timestamp(struct mlx4_en_dev *mdev)
&mdev->pdev->dev);
if (IS_ERR(mdev->ptp_clock)) {
mdev->ptp_clock = NULL;
+ kfree(mdev->clock);
mlx4_err(mdev, "ptp_clock_register failed\n");
} else {
mlx4_info(mdev, "registered PHC clock\n");
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index e7733c1..7d1d460 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -379,7 +379,7 @@ struct mlx4_en_dev {
spinlock_t clock_lock;
u32 nominal_c_mult;
struct cyclecounter cycles;
- struct timecounter clock;
+ struct timecounter *clock;
unsigned long last_overflow_check;
unsigned long overflow_period;
struct ptp_clock *ptp_clock;
--
1.7.8.2
--
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