On Mon, 14 Apr 2025 22:54:41 +0200
Borislav Petkov <[email protected]> wrote:
> On Mon, Apr 14, 2025 at 03:35:41PM -0500, Junxuan Liao wrote:
> > Rename page_fault_{user,kernel} to page_fault_{user,kernel}_enter, and
> > add the exit counterparts. This might be useful for measuring page fault
> ^^^^^^^^^^^^^^^^
>
> Well, come back when it really becomes useful.
It's useful for me ;-)
# cd /sys/kernel/tracing
# echo 's:user_faults u64 delta;' >> dynamic_events
# echo 'hist:keys=common_pid:ts0=common_timestamp.usecs' >>
events/exceptions/page_fault_user_enter/trigger
# echo
'hist:keys=common_pid:delta=common_timestamp.usecs-$ts0:onmatch(exceptions.page_fault_user_enter).trace(user_faults,$delta)'
>> events/exceptions/page_fault_user_exit/trigger
# cd /work/git/trace-cmd.git
# echo 'hist:keys=delta.log2:sort=delta if COMM == "cc1"' >
/sys/kernel/tracing/events/synthetic/user_faults/trigger
# make
[..]
# cat /sys/kernel/tracing/events/synthetic/user_faults/hist
# event histogram
#
# trigger info: hist:keys=delta.log2:vals=hitcount:sort=delta.log2:size=2048 if
COMM == "cc1" [active]
#
{ delta: ~ 2^0 } hitcount: 1
{ delta: ~ 2^1 } hitcount: 334
{ delta: ~ 2^2 } hitcount: 4090
{ delta: ~ 2^3 } hitcount: 86037
{ delta: ~ 2^4 } hitcount: 108790
{ delta: ~ 2^5 } hitcount: 27387
{ delta: ~ 2^6 } hitcount: 6015
{ delta: ~ 2^7 } hitcount: 481
{ delta: ~ 2^8 } hitcount: 134
{ delta: ~ 2^9 } hitcount: 74
{ delta: ~ 2^10 } hitcount: 54
{ delta: ~ 2^11 } hitcount: 6
Totals:
Hits: 233403
Entries: 12
Dropped: 0
The above shows a histogram in microseconds where the buckets increase in a
power of two. The biggest bucket is between 2^4 (16) and 2^5 (32) microseconds
with 108790 hits.
The longest bucket of 2^11 (2ms) to 2^12 (4ms) had 6 hits.
And when sframes is supported, it will be able to show the user space stack
trace of where the longest page faults occur.
-- Steve
