diff mbox series

[RFC,net-next,4/4] net: stmmac: remove unnecessary locking around PTP clock reads

Message ID 20211210193556.1349090-5-yannick.vignon@oss.nxp.com (mailing list archive)
State RFC
Delegated to: Netdev Maintainers
Headers show
Series net: Improving network scheduling latencies | expand

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Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit fail Errors and warnings before: 0 this patch: 1
netdev/cc_maintainers warning 4 maintainers not CCed: linux-arm-kernel@lists.infradead.org linux-stm32@st-md-mailman.stormreply.com mcoquelin.stm32@gmail.com alexandre.torgue@foss.st.com
netdev/build_clang fail Errors and warnings before: 0 this patch: 2
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn fail Errors and warnings before: 0 this patch: 1
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 9 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Yannick Vignon Dec. 10, 2021, 7:35 p.m. UTC 
From: Yannick Vignon <yannick.vignon@nxp.com>

Reading the PTP clock is a simple operation requiring only 2 register reads,
while the time can be set atomically through another set of registers. Under
a PREEMPT_RT kernel, protecting the reads by a spin_lock is
counter-productive:
 * if the task is preempted in-between the 2 reads, the return time value
could become inconsistent,
 * if the 2nd task preempting the 1st has a higher prio but needs to
read time as well, it will require 2 costly context switches, which
will pretty much always be more costly than disabling preemption with a real
spin_lock.

Remove the unneeded locking around the gettime call.

Signed-off-by: Yannick Vignon <yannick.vignon@nxp.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c | 2 --
 1 file changed, 2 deletions(-)
diff mbox series

Patch

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
index 580cc035536b..8f0dcac23b1e 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
@@ -137,9 +137,7 @@  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);
 	stmmac_get_systime(priv, priv->ptpaddr, &ns);
-	spin_unlock_irqrestore(&priv->ptp_lock, flags);
 
 	*ts = ns_to_timespec64(ns);