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Date: Fri, 4 Feb 2022 14:55:44 +0100
From: Yannick Vignon <yannick.vignon@....nxp.com>
To: Giuseppe Cavallaro <peppe.cavallaro@...com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Jose Abreu <joabreu@...opsys.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
netdev@...r.kernel.org, Vladimir Oltean <olteanv@...il.com>,
Xiaoliang Yang <xiaoliang.yang_1@....com>, mingkai.hu@....com,
Joakim Zhang <qiangqing.zhang@....com>,
sebastien.laveze@....com
Cc: Yannick Vignon <yannick.vignon@....com>
Subject: [PATCH net-next] net: stmmac: optimize locking around PTP clock reads
From: Yannick Vignon <yannick.vignon@....com>
Reading the PTP clock is a simple operation requiring only 3 register
reads. Under a PREEMPT_RT kernel, protecting those reads by a spin_lock is
counter-productive: if the 2nd task preempting the 1st has a higher prio
but needs to read time as well, it will require 2 context switches, which
will pretty much always be more costly than just disabling preemption for
the duration of the reads. Moreover, with the code logic recently added
to get_systime(), disabling preemption is not even required anymore:
reads and writes just need to be protected from each other, to prevent a
clock read while the clock is being updated.
Improve the above situation by replacing the PTP spinlock by a rwlock, and
using read_lock for PTP clock reads so simultaneous reads do not block
each other.
Signed-off-by: Yannick Vignon <yannick.vignon@....com>
---
.../net/ethernet/stmicro/stmmac/dwmac-intel.c | 4 ++--
drivers/net/ethernet/stmicro/stmmac/stmmac.h | 2 +-
.../ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 4 ++--
.../net/ethernet/stmicro/stmmac/stmmac_ptp.c | 22 +++++++++----------
.../stmicro/stmmac/stmmac_selftests.c | 8 +++----
5 files changed, 20 insertions(+), 20 deletions(-)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c
index 8e8778cfbbad..5943ff9f21c2 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c
@@ -383,10 +383,10 @@ static int intel_crosststamp(ktime_t *device,
/* Repeat until the timestamps are from the FIFO last segment */
for (i = 0; i < num_snapshot; i++) {
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ read_lock_irqsave(&priv->ptp_lock, flags);
stmmac_get_ptptime(priv, ptpaddr, &ptp_time);
*device = ns_to_ktime(ptp_time);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ read_unlock_irqrestore(&priv->ptp_lock, flags);
get_arttime(priv->mii, intel_priv->mdio_adhoc_addr, &art_time);
*system = convert_art_to_tsc(art_time);
}
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 5b195d5051d6..57970ae2178d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -263,7 +263,7 @@ struct stmmac_priv {
u32 adv_ts;
int use_riwt;
int irq_wake;
- spinlock_t ptp_lock;
+ rwlock_t ptp_lock;
/* Protects auxiliary snapshot registers from concurrent access. */
struct mutex aux_ts_lock;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
index a7ec9f4d46ce..22fea0f67245 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
@@ -196,9 +196,9 @@ static void timestamp_interrupt(struct stmmac_priv *priv)
GMAC_TIMESTAMP_ATSNS_SHIFT;
for (i = 0; i < num_snapshot; i++) {
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ read_lock_irqsave(&priv->ptp_lock, flags);
get_ptptime(priv->ptpaddr, &ptp_time);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ read_unlock_irqrestore(&priv->ptp_lock, flags);
event.type = PTP_CLOCK_EXTTS;
event.index = 0;
event.timestamp = ptp_time;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
index 1c9f02f9c317..e45fb191d8e6 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
@@ -39,9 +39,9 @@ static int stmmac_adjust_freq(struct ptp_clock_info *ptp, s32 ppb)
diff = div_u64(adj, 1000000000ULL);
addend = neg_adj ? (addend - diff) : (addend + diff);
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ write_lock_irqsave(&priv->ptp_lock, flags);
stmmac_config_addend(priv, priv->ptpaddr, addend);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ write_unlock_irqrestore(&priv->ptp_lock, flags);
return 0;
}
@@ -86,9 +86,9 @@ static int stmmac_adjust_time(struct ptp_clock_info *ptp, s64 delta)
mutex_unlock(&priv->plat->est->lock);
}
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ write_lock_irqsave(&priv->ptp_lock, flags);
stmmac_adjust_systime(priv, priv->ptpaddr, sec, nsec, neg_adj, xmac);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ write_unlock_irqrestore(&priv->ptp_lock, flags);
/* Caculate new basetime and re-configured EST after PTP time adjust. */
if (est_rst) {
@@ -137,9 +137,9 @@ static int stmmac_get_time(struct ptp_clock_info *ptp, struct timespec64 *ts)
unsigned long flags;
u64 ns = 0;
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ read_lock_irqsave(&priv->ptp_lock, flags);
stmmac_get_systime(priv, priv->ptpaddr, &ns);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ read_unlock_irqrestore(&priv->ptp_lock, flags);
*ts = ns_to_timespec64(ns);
@@ -162,9 +162,9 @@ static int stmmac_set_time(struct ptp_clock_info *ptp,
container_of(ptp, struct stmmac_priv, ptp_clock_ops);
unsigned long flags;
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ write_lock_irqsave(&priv->ptp_lock, flags);
stmmac_init_systime(priv, priv->ptpaddr, ts->tv_sec, ts->tv_nsec);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ write_unlock_irqrestore(&priv->ptp_lock, flags);
return 0;
}
@@ -194,12 +194,12 @@ static int stmmac_enable(struct ptp_clock_info *ptp,
cfg->period.tv_sec = rq->perout.period.sec;
cfg->period.tv_nsec = rq->perout.period.nsec;
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ write_lock_irqsave(&priv->ptp_lock, flags);
ret = stmmac_flex_pps_config(priv, priv->ioaddr,
rq->perout.index, cfg, on,
priv->sub_second_inc,
priv->systime_flags);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ write_unlock_irqrestore(&priv->ptp_lock, flags);
break;
case PTP_CLK_REQ_EXTTS:
priv->plat->ext_snapshot_en = on;
@@ -314,7 +314,7 @@ void stmmac_ptp_register(struct stmmac_priv *priv)
stmmac_ptp_clock_ops.n_per_out = priv->dma_cap.pps_out_num;
stmmac_ptp_clock_ops.n_ext_ts = priv->dma_cap.aux_snapshot_n;
- spin_lock_init(&priv->ptp_lock);
+ rwlock_init(&priv->ptp_lock);
mutex_init(&priv->aux_ts_lock);
priv->ptp_clock_ops = stmmac_ptp_clock_ops;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
index be3cb63675a5..9f1759593b94 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
@@ -1777,9 +1777,9 @@ static int stmmac_test_tbs(struct stmmac_priv *priv)
if (ret)
return ret;
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ read_lock_irqsave(&priv->ptp_lock, flags);
stmmac_get_systime(priv, priv->ptpaddr, &curr_time);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ read_unlock_irqrestore(&priv->ptp_lock, flags);
if (!curr_time) {
ret = -EOPNOTSUPP;
@@ -1799,9 +1799,9 @@ static int stmmac_test_tbs(struct stmmac_priv *priv)
goto fail_disable;
/* Check if expected time has elapsed */
- spin_lock_irqsave(&priv->ptp_lock, flags);
+ read_lock_irqsave(&priv->ptp_lock, flags);
stmmac_get_systime(priv, priv->ptpaddr, &curr_time);
- spin_unlock_irqrestore(&priv->ptp_lock, flags);
+ read_unlock_irqrestore(&priv->ptp_lock, flags);
if ((curr_time - start_time) < STMMAC_TBS_LT_OFFSET)
ret = -EINVAL;
--
2.25.1
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