Hi Greg,
On Mon, Dec 14, 2020 at 03:25:53PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 5.4-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 <stable@xxxxxxxxxxxxxxx>.
Here is the backport with abe8f12b4425 ("x86/resctrl: Remove unused struct mbm_state::chunks_bw")
which makes the backport easy.
--
Regards
Sudip
>From 588bb4819bd29978d16081fd50f6c1d99d95b234 Mon Sep 17 00:00:00 2001
From: James Morse <james.morse@xxxxxxx>
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.
Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20200708163929.2783-2-james.morse@xxxxxxx
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
---
arch/x86/kernel/cpu/resctrl/internal.h | 2 --
arch/x86/kernel/cpu/resctrl/monitor.c | 3 +--
2 files changed, 1 insertion(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 17095435c875..499cb2e727a0 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -276,7 +276,6 @@ 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
@@ -285,7 +284,6 @@ struct rftype {
struct mbm_state {
u64 chunks;
u64 prev_msr;
- u64 chunks_bw;
u64 prev_bw_msr;
u32 prev_bw;
u32 delta_bw;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 0cf4f87f6012..f62db1353945 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -280,8 +280,7 @@ 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 6e4bf9f372b1c0fa200ac473979456db8c104d0d Mon Sep 17 00:00:00 2001
From: Xiaochen Shen <xiaochen.shen@xxxxxxxxx>
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
Fixes: ba0f26d8529c (x86/intel_rdt/mba_sc: Prepare for feedback loop)
Signed-off-by: Xiaochen Shen <xiaochen.shen@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/1607063279-19437-1-git-send-email-xiaochen.shen@xxxxxxxxx
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
---
arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index f62db1353945..50f683ecd2c6 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -280,7 +280,6 @@ 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)
@@ -450,15 +449,14 @@ 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
