FAILED: patch "[PATCH] x86/resctrl: Fix incorrect local bandwidth when mba_sc is" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 06c5fe9b12dde1b62821f302f177c972bb1c81f9 Mon Sep 17 00:00:00 2001
From: Xiaochen Shen <[email protected]>
Date: Fri, 4 Dec 2020 14:27:59 +0800
Subject: [PATCH] x86/resctrl: Fix incorrect local bandwidth when mba_sc is
enabled

The MBA software controller (mba_sc) is a feedback loop which periodically reads MBM counters and tries to restrict the bandwidth below a user-specified value. It tags along the MBM counter overflow handler to do the updates with 1s interval in mbm_update() and update_mba_bw().

The purpose of mbm_update() is to periodically read the MBM counters to make sure that the hardware counter doesn't wrap around more than once between user samplings. mbm_update() calls __mon_event_count() for local bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count() instead when mba_sc is enabled. __mon_event_count() will not be called for local bandwidth updating in MBM counter overflow handler, but it is still called when reading MBM local bandwidth counter file 'mbm_local_bytes', the call path is as below:

rdtgroup_mondata_show()

    mon_event_read()
      mon_event_count()
        __mon_event_count()

In __mon_event_count(), m->chunks is updated by delta chunks which is calculated from previous MSR value (m->prev_msr) and current MSR value. When mba_sc is enabled, m->chunks is also updated in mbm_update() by mistake by the delta chunks which is calculated from m->prev_bw_msr instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in the mba_sc feedback loop.

When reading MBM local bandwidth counter file, m->chunks was changed unexpectedly by mbm_bw_count(). As a result, the incorrect local bandwidth counter which calculated from incorrect m->chunks is shown to the user.

Fix this by removing incorrect m->chunks updating in mbm_bw_count() in MBM counter overflow handler, and always calling __mon_event_count() in mbm_update() to make sure that the hardware local bandwidth counter doesn't wrap around.

Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s) git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat && make
./tools/membw/membw -c 0 -b 10000 --read

# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl

# Create control group c1
mkdir /sys/fs/resctrl/c1

# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata

# Write PID of the workload to tasks file
echo pidof membw > /sys/fs/resctrl/c1/tasks

# Read local bytes counters twice with 1s interval, the calculated

  # local bandwidth is not as expected (approaching to 6 GB/s):
  local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  sleep 1
  local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  echo "local b/w (bytes/s):" `expr $local_2 - $local_1`

Before fix:
local b/w (bytes/s): 11076796416

After fix:
local b/w (bytes/s): 5465014272

index 54dffe574e67..a98519a3a2e6 100644
@@ -279,7 +279,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
 		return;
 
 	chunks = mbm_overflow_count(m->prev_bw_msr, tval, rr->r->mbm_width);
-	m->chunks += chunks;
 	cur_bw = (chunks * r->mon_scale) >> 20;
 
 	if (m->delta_comp)

@@ -450,15 +449,14 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
 	}
 	if (is_mbm_local_enabled()) {
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+		__mon_event_count(rmid, &rr);
 
 		/*
 		 * Call the MBA software controller only for the
 		 * control groups and when user has enabled
 		 * the software controller explicitly.
 		 */
-		if (!is_mba_sc(NULL))
-			__mon_event_count(rmid, &rr);
-		else
+		if (is_mba_sc(NULL))
 			mbm_bw_count(rmid, &rr);
 	}
 }

commit 06c5fe9b12dde1b62821f302f177c972bb1c81f9 upstream.

The MBA software controller (mba_sc) is a feedback loop which periodically reads MBM counters and tries to restrict the bandwidth below a user-specified value. It tags along the MBM counter overflow handler to do the updates with 1s interval in mbm_update() and update_mba_bw().

The purpose of mbm_update() is to periodically read the MBM counters to make sure that the hardware counter doesn't wrap around more than once between user samplings. mbm_update() calls __mon_event_count() for local bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count() instead when mba_sc is enabled. __mon_event_count() will not be called for local bandwidth updating in MBM counter overflow handler, but it is still called when reading MBM local bandwidth counter file 'mbm_local_bytes', the call path is as below:

rdtgroup_mondata_show()

    mon_event_read()
      mon_event_count()
        __mon_event_count()

In __mon_event_count(), m->chunks is updated by delta chunks which is calculated from previous MSR value (m->prev_msr) and current MSR value. When mba_sc is enabled, m->chunks is also updated in mbm_update() by mistake by the delta chunks which is calculated from m->prev_bw_msr instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in the mba_sc feedback loop.

When reading MBM local bandwidth counter file, m->chunks was changed unexpectedly by mbm_bw_count(). As a result, the incorrect local bandwidth counter which calculated from incorrect m->chunks is shown to the user.

Fix this by removing incorrect m->chunks updating in mbm_bw_count() in MBM counter overflow handler, and always calling __mon_event_count() in mbm_update() to make sure that the hardware local bandwidth counter doesn't wrap around.

Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s) git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat && make
./tools/membw/membw -c 0 -b 10000 --read

# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl

# Create control group c1
mkdir /sys/fs/resctrl/c1

# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata

# Write PID of the workload to tasks file
echo pidof membw > /sys/fs/resctrl/c1/tasks

# Read local bytes counters twice with 1s interval, the calculated

  # local bandwidth is not as expected (approaching to 6 GB/s):
  local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  sleep 1
  local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  echo "local b/w (bytes/s):" `expr $local_2 - $local_1`

Before fix:
local b/w (bytes/s): 11076796416

After fix:
local b/w (bytes/s): 5465014272

Backporting notes:

Since upstream commit fa7d949337cc ("x86/resctrl: Rename and move rdt files to a separate directory"), the file arch/x86/kernel/cpu/intel_rdt_monitor.c has been renamed and moved to arch/x86/kernel/cpu/resctrl/monitor.c.
Apply the change against file arch/x86/kernel/cpu/intel_rdt_monitor.c for older stable trees.

Upstream commit abe8f12b4425 ("x86/resctrl: Remove unused struct mbm_state::chunks_bw") removed unused struct mbm_state::chunks_bw. It changes the code base in mbm_bw_count().
Apply the change against the code base in older stable trees.

---
 arch/x86/kernel/cpu/intel_rdt_monitor.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

index 3d4ec80..344e049 100644
@@ -291,7 +291,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
 
 	chunks = mbm_overflow_count(m->prev_bw_msr, tval);
 	m->chunks_bw += chunks;
-	m->chunks = m->chunks_bw;
 	cur_bw = (chunks * r->mon_scale) >> 20;
 
 	if (m->delta_comp)

@@ -461,15 +460,14 @@ static void mbm_update(struct rdt_domain *d, int rmid)
 	}
 	if (is_mbm_local_enabled()) {
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+		__mon_event_count(rmid, &rr);
 
 		/*
 		 * Call the MBA software controller only for the
 		 * control groups and when user has enabled
 		 * the software controller explicitly.
 		 */
-		if (!is_mba_sc(NULL))
-			__mon_event_count(rmid, &rr);
-		else
+		if (is_mba_sc(NULL))
 			mbm_bw_count(rmid, &rr);
 	}
 }

1.8.3.1

Hi Greg,

Here is the backport with abe8f12b4425 ("x86/resctrl: Remove unused struct mbm_state::chunks_bw") which makes the backport easy.

--
Regards
Sudip

From 269df62e154d3f7a5bed22b81e0a6389530bf078 Mon Sep 17 00:00:00 2001
From: James Morse <[email protected]>
Date: Wed, 8 Jul 2020 16:39:20 +0000
Subject: [PATCH 1/2] x86/resctrl: Remove unused struct mbm_state::chunks_bw

commit abe8f12b44250d02937665033a8b750c1bfeb26e upstream

Nothing reads struct mbm_states's chunks_bw value, its a copy of chunks. Remove it.

---
 arch/x86/kernel/cpu/intel_rdt.h         | 2 --
 arch/x86/kernel/cpu/intel_rdt_monitor.c | 3 +--
 2 files changed, 1 insertion(+), 4 deletions(-)

index 2b483b739cf1..8412234eabd3 100644
@@ -251,7 +251,6 @@ struct rftype {
  * struct mbm_state - status for each MBM counter in each domain
  * @chunks:	Total data moved (multiply by rdt_group.mon_scale to get bytes)
  * @prev_msr	Value of IA32_QM_CTR for this RMID last time we read it
- * @chunks_bw	Total local data moved. Used for bandwidth calculation
  * @prev_bw_msr:Value of previous IA32_QM_CTR for bandwidth counting
  * @prev_bw	The most recent bandwidth in MBps
  * @delta_bw	Difference between the current and previous bandwidth

@@ -260,7 +259,6 @@ struct rftype {
 struct mbm_state {
 	u64	chunks;
 	u64	prev_msr;
-	u64	chunks_bw;
 	u64	prev_bw_msr;
 	u32	prev_bw;
 	u32	delta_bw;

index 3d4ec80a6bb9..a9f25200fc0f 100644
@@ -290,8 +290,7 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
 		return;
 
 	chunks = mbm_overflow_count(m->prev_bw_msr, tval);
-	m->chunks_bw += chunks;
-	m->chunks = m->chunks_bw;
+	m->chunks += chunks;
 	cur_bw = (chunks * r->mon_scale) >> 20;
 
 	if (m->delta_comp)

2.11.0

From 91dd29a5524e8c5547ff9dda0c858cc2aeb54ccc Mon Sep 17 00:00:00 2001
From: Xiaochen Shen <[email protected]>
Date: Fri, 4 Dec 2020 14:27:59 +0800
Subject: [PATCH 2/2] x86/resctrl: Fix incorrect local bandwidth when mba_sc is enabled

commit 06c5fe9b12dde1b62821f302f177c972bb1c81f9 upstream

The MBA software controller (mba_sc) is a feedback loop which periodically reads MBM counters and tries to restrict the bandwidth below a user-specified value. It tags along the MBM counter overflow handler to do the updates with 1s interval in mbm_update() and update_mba_bw().

The purpose of mbm_update() is to periodically read the MBM counters to make sure that the hardware counter doesn't wrap around more than once between user samplings. mbm_update() calls __mon_event_count() for local bandwidth updating when mba_sc is not enabled, but calls mbm_bw_count() instead when mba_sc is enabled. __mon_event_count() will not be called for local bandwidth updating in MBM counter overflow handler, but it is still called when reading MBM local bandwidth counter file 'mbm_local_bytes', the call path is as below:

rdtgroup_mondata_show()

    mon_event_read()
      mon_event_count()
        __mon_event_count()

In __mon_event_count(), m->chunks is updated by delta chunks which is calculated from previous MSR value (m->prev_msr) and current MSR value. When mba_sc is enabled, m->chunks is also updated in mbm_update() by mistake by the delta chunks which is calculated from m->prev_bw_msr instead of m->prev_msr. But m->chunks is not used in update_mba_bw() in the mba_sc feedback loop.

When reading MBM local bandwidth counter file, m->chunks was changed unexpectedly by mbm_bw_count(). As a result, the incorrect local bandwidth counter which calculated from incorrect m->chunks is shown to the user.

Fix this by removing incorrect m->chunks updating in mbm_bw_count() in MBM counter overflow handler, and always calling __mon_event_count() in mbm_update() to make sure that the hardware local bandwidth counter doesn't wrap around.

Test steps:
# Run workload with aggressive memory bandwidth (e.g., 10 GB/s) git clone https://github.com/intel/intel-cmt-cat && cd intel-cmt-cat && make
./tools/membw/membw -c 0 -b 10000 --read

# Enable MBA software controller
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl

# Create control group c1
mkdir /sys/fs/resctrl/c1

# Set MB throttle to 6 GB/s
echo "MB:0=6000;1=6000" > /sys/fs/resctrl/c1/schemata

# Write PID of the workload to tasks file
echo pidof membw > /sys/fs/resctrl/c1/tasks

# Read local bytes counters twice with 1s interval, the calculated

  # local bandwidth is not as expected (approaching to 6 GB/s):
  local_1=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  sleep 1
  local_2=`cat /sys/fs/resctrl/c1/mon_data/mon_L3_00/mbm_local_bytes`
  echo "local b/w (bytes/s):" `expr $local_2 - $local_1`

Before fix:
local b/w (bytes/s): 11076796416

After fix:
local b/w (bytes/s): 5465014272

---
 arch/x86/kernel/cpu/intel_rdt_monitor.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

index a9f25200fc0f..5dfa5ab9a5ae 100644
@@ -290,7 +290,6 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
 		return;
 
 	chunks = mbm_overflow_count(m->prev_bw_msr, tval);
-	m->chunks += chunks;
 	cur_bw = (chunks * r->mon_scale) >> 20;
 
 	if (m->delta_comp)

@@ -460,15 +459,14 @@ static void mbm_update(struct rdt_domain *d, int rmid)
 	}
 	if (is_mbm_local_enabled()) {
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
+		__mon_event_count(rmid, &rr);
 
 		/*
 		 * Call the MBA software controller only for the
 		 * control groups and when user has enabled
 		 * the software controller explicitly.
 		 */
-		if (!is_mba_sc(NULL))
-			__mon_event_count(rmid, &rr);
-		else
+		if (is_mba_sc(NULL))
 			mbm_bw_count(rmid, &rr);
 	}
 }

2.11.0