From 642436a1ad34a28c45bbc2bdc131640a73782356 Mon Sep 17 00:00:00 2001 From: Yannick Vignon Date: Fri, 4 Feb 2022 14:55:44 +0100 Subject: net: stmmac: optimize locking around PTP clock reads 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 Link: https://lore.kernel.org/r/20220204135545.2770625-1-yannick.vignon@oss.nxp.com Signed-off-by: Jakub Kicinski --- drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/net/ethernet/stmicro/stmmac/dwmac-intel.c') 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); } -- cgit v1.2.3