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Message-ID: <20240325232039.76836-3-mschmidt@redhat.com>
Date: Tue, 26 Mar 2024 00:20:38 +0100
From: Michal Schmidt <mschmidt@...hat.com>
To: intel-wired-lan@...ts.osuosl.org
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
Tony Nguyen <anthony.l.nguyen@...el.com>,
Richard Cochran <richardcochran@...il.com>,
netdev@...r.kernel.org,
Jacob Keller <jacob.e.keller@...el.com>,
Jiri Pirko <jiri@...nulli.us>,
Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
Karol Kolacinski <karol.kolacinski@...el.com>,
Marcin Szycik <marcin.szycik@...ux.intel.com>,
Przemek Kitszel <przemyslaw.kitszel@...el.com>,
"Temerkhanov, Sergey" <sergey.temerkhanov@...el.com>
Subject: [PATCH net-next v4 2/3] ice: avoid the PTP hardware semaphore in gettimex64 path
The PTP hardware semaphore (PFTSYN_SEM) is used to synchronize
operations that program the PTP timers. The operations involve issuing
commands to the sideband queue. The E810 does not have a hardware
sideband queue, so the admin queue is used. The admin queue is slow.
I have observed delays in hundreds of milliseconds waiting for
ice_sq_done.
When phc2sys reads the time from the ice PTP clock and PFTSYN_SEM is
held by a task performing one of the slow operations, ice_ptp_lock can
easily time out. phc2sys gets -EBUSY and the kernel prints:
ice 0000:XX:YY.0: PTP failed to get time
These messages appear once every few seconds, causing log spam.
The E810 datasheet recommends an algorithm for reading the upper 64 bits
of the GLTSYN_TIME register. It matches what's implemented in
ice_ptp_read_src_clk_reg. It is robust against wrap-around, but not
necessarily against the concurrent setting of the register (with
GLTSYN_CMD_{INIT,ADJ}_TIME commands). Perhaps that's why
ice_ptp_gettimex64 also takes PFTSYN_SEM.
The race with time setters can be prevented without relying on the PTP
hardware semaphore. Using the "ice_adapter" from the previous patch,
we can have a common spinlock for the PFs that share the clock hardware.
It will protect the reading and writing to the GLTSYN_TIME register.
The writing is performed indirectly, by the hardware, as a result of
the driver writing GLTSYN_CMD_SYNC in ice_ptp_exec_tmr_cmd. I wasn't
sure if the ice_flush there is enough to make sure GLTSYN_TIME has been
updated, but it works well in my testing.
My test code can be seen here:
https://gitlab.com/mschmidt2/linux/-/commits/ice-ptp-host-side-lock-10
It consists of:
- kernel threads reading the time in a busy loop and looking at the
deltas between consecutive values, reporting new maxima.
- a shell script that sets the time repeatedly;
- a bpftrace probe to produce a histogram of the measured deltas.
Without the spinlock ptp_gltsyn_time_lock, it is easy to see tearing.
Deltas in the [2G, 4G) range appear in the histograms.
With the spinlock added, there is no tearing and the biggest delta I saw
was in the range [1M, 2M), that is under 2 ms.
Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Signed-off-by: Michal Schmidt <mschmidt@...hat.com>
---
drivers/net/ethernet/intel/ice/ice_adapter.c | 2 ++
drivers/net/ethernet/intel/ice/ice_adapter.h | 6 ++++++
drivers/net/ethernet/intel/ice/ice_ptp.c | 8 +-------
drivers/net/ethernet/intel/ice/ice_ptp_hw.c | 3 +++
4 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/net/ethernet/intel/ice/ice_adapter.c b/drivers/net/ethernet/intel/ice/ice_adapter.c
index f00ab998e853..52d15ef7f4b1 100644
--- a/drivers/net/ethernet/intel/ice/ice_adapter.c
+++ b/drivers/net/ethernet/intel/ice/ice_adapter.c
@@ -6,6 +6,7 @@
#include <linux/mutex.h>
#include <linux/pci.h>
#include <linux/slab.h>
+#include <linux/spinlock.h>
#include <linux/xarray.h>
#include "ice_adapter.h"
@@ -35,6 +36,7 @@ static struct ice_adapter *ice_adapter_new(void)
if (!adapter)
return NULL;
+ spin_lock_init(&adapter->ptp_gltsyn_time_lock);
refcount_set(&adapter->refcount, 1);
return adapter;
diff --git a/drivers/net/ethernet/intel/ice/ice_adapter.h b/drivers/net/ethernet/intel/ice/ice_adapter.h
index cb5a02eb24c1..9d11014ec02f 100644
--- a/drivers/net/ethernet/intel/ice/ice_adapter.h
+++ b/drivers/net/ethernet/intel/ice/ice_adapter.h
@@ -4,15 +4,21 @@
#ifndef _ICE_ADAPTER_H_
#define _ICE_ADAPTER_H_
+#include <linux/spinlock_types.h>
#include <linux/refcount_types.h>
struct pci_dev;
/**
* struct ice_adapter - PCI adapter resources shared across PFs
+ * @ptp_gltsyn_time_lock: Spinlock protecting access to the GLTSYN_TIME
+ * register of the PTP clock.
* @refcount: Reference count. struct ice_pf objects hold the references.
*/
struct ice_adapter {
+ /* For access to the GLTSYN_TIME register */
+ spinlock_t ptp_gltsyn_time_lock;
+
refcount_t refcount;
};
diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c
index c11eba07283c..0875f37add78 100644
--- a/drivers/net/ethernet/intel/ice/ice_ptp.c
+++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
@@ -374,6 +374,7 @@ ice_ptp_read_src_clk_reg(struct ice_pf *pf, struct ptp_system_timestamp *sts)
u8 tmr_idx;
tmr_idx = ice_get_ptp_src_clock_index(hw);
+ guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock);
/* Read the system timestamp pre PHC read */
ptp_read_system_prets(sts);
@@ -1925,15 +1926,8 @@ ice_ptp_gettimex64(struct ptp_clock_info *info, struct timespec64 *ts,
struct ptp_system_timestamp *sts)
{
struct ice_pf *pf = ptp_info_to_pf(info);
- struct ice_hw *hw = &pf->hw;
-
- if (!ice_ptp_lock(hw)) {
- dev_err(ice_pf_to_dev(pf), "PTP failed to get time\n");
- return -EBUSY;
- }
ice_ptp_read_time(pf, ts, sts);
- ice_ptp_unlock(hw);
return 0;
}
diff --git a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
index 187ce9b54e1a..2b9423a173bb 100644
--- a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
+++ b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
@@ -274,6 +274,9 @@ void ice_ptp_src_cmd(struct ice_hw *hw, enum ice_ptp_tmr_cmd cmd)
*/
static void ice_ptp_exec_tmr_cmd(struct ice_hw *hw)
{
+ struct ice_pf *pf = container_of(hw, struct ice_pf, hw);
+
+ guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock);
wr32(hw, GLTSYN_CMD_SYNC, SYNC_EXEC_CMD);
ice_flush(hw);
}
--
2.43.2
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