The following commit has been merged into the x86/cache branch of tip:
Commit-ID: 2ba836dbe2467d31fffb439258c2f454c6f1a317
Gitweb:
https://git.kernel.org/tip/2ba836dbe2467d31fffb439258c2f454c6f1a317
Author: Xiaochen Shen <xiaochen.s...@intel.com>
AuthorDate: Fri, 04 Dec 2020 14:27:59 +08:00
Committer: Borislav Petkov <b...@suse.de>
CommitterDate: Wed, 09 Dec 2020 20:00:46 +01:00
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 bandwidth. 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 using 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.s...@intel.com>
Signed-off-by: Borislav Petkov <b...@suse.de>
Reviewed-by: Tony Luck <tony.l...@intel.com>
Link:
https://lkml.kernel.org/r/1607063279-19437-1-git-send-email-xiaochen.s...@intel.com
---
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 622073f..93a33b7 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -320,7 +320,6 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
}
chunks = mbm_overflow_count(m->prev_msr, tval, rr->r->mbm_width);
- m->chunks += chunks;
m->prev_msr = tval;
rr->val += get_corrected_mbm_count(rmid, m->chunks);
@@ -514,15 +513,14 @@ 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);
}
}
