Ubuntu Manpage: perf-mem - Profile memory accesses

Provided by: linux-perf_6.16.0-13.13_amd64

NAME

       perf-mem - Profile memory accesses

SYNOPSIS

       perf mem [<options>] (record [<command>] | report)

DESCRIPTION

       "perf mem record" runs a command and gathers memory operation data from it, into perf.data. Perf record
       options are accepted and are passed through.

       "perf mem report" displays the result. It invokes perf report with the right set of options to display a
       memory access profile. By default, loads and stores are sampled. Use the -t option to limit to loads or
       stores.

       Note that on Intel systems the memory latency reported is the use-latency, not the pure load (or store
       latency). Use latency includes any pipeline queuing delays in addition to the memory subsystem latency.

       On Arm64 this uses SPE to sample load and store operations, therefore hardware and kernel support is
       required. See perf-arm-spe(1) for a setup guide. Due to the statistical nature of SPE sampling, not every
       memory operation will be sampled.

       On AMD this use IBS Op PMU to sample load-store operations.

COMMON OPTIONS

       -f, --force
           Don’t do ownership validation

       -t, --type=<type>
           Select the memory operation type: load or store (default: load,store)

       -v, --verbose
           Be more verbose (show counter open errors, etc)

       -p, --phys-data
           Record/Report sample physical addresses

       --data-page-size
           Record/Report sample data address page size

RECORD OPTIONS

       <command>...
           Any command you can specify in a shell.

       -e, --event <event>
           Event selector. Use perf mem record -e list to list available events.

       -K, --all-kernel
           Configure all used events to run in kernel space.

       -U, --all-user
           Configure all used events to run in user space.

       --ldlat <n>
           Specify desired latency for loads event. Supported on Intel, Arm64 and some AMD processors. Ignored
           on other archs.

               On supported AMD processors:
               - /sys/bus/event_source/devices/ibs_op/caps/ldlat file contains '1'.
               - Supported latency values are 128 to 2048 (both inclusive).
               - Latency value which is a multiple of 128 incurs a little less profiling
                 overhead compared to other values.
               - Load latency filtering is disabled by default.

REPORT OPTIONS

-i, --input=<file>
Input file name.

-C, --cpu=<cpu>
Monitor only on the list of CPUs provided. Multiple CPUs can be provided as a comma-separated list
with no space: 0,1. Ranges of CPUs are specified with - like 0-2. Default is to monitor all CPUS.

-D, --dump-raw-samples
Dump the raw decoded samples on the screen in a format that is easy to parse with one sample per
line.

-s, --sort=<key>
Group result by given key(s) - multiple keys can be specified in CSV format. The keys are specific to
memory samples are: symbol_daddr, symbol_iaddr, dso_daddr, locked, tlb, mem, snoop, dcacheline,
phys_daddr, data_page_size, blocked.

• symbol_daddr: name of data symbol being executed on at the time of sample

• symbol_iaddr: name of code symbol being executed on at the time of sample

• dso_daddr: name of library or module containing the data being executed on at the time of the
sample

• locked: whether the bus was locked at the time of the sample

• tlb: type of tlb access for the data at the time of the sample

• mem: type of memory access for the data at the time of the sample

• snoop: type of snoop (if any) for the data at the time of the sample

• dcacheline: the cacheline the data address is on at the time of the sample

• phys_daddr: physical address of data being executed on at the time of sample

• data_page_size: the data page size of data being executed on at the time of sample

• blocked: reason of blocked load access for the data at the time of the sample

And the default sort keys are changed to local_weight, mem, sym, dso,
symbol_daddr, dso_daddr, snoop, tlb, locked, blocked, local_ins_lat.

-F, --fields=
Specify output field - multiple keys can be specified in CSV format. Please see perf-report(1) for
details.

In addition to the default fields, 'perf mem report' will provide the
following fields to break down sample periods.

• op: operation in the sample instruction (load, store, prefetch, ...)

• cache: location in CPU cache (L1, L2, ...) where the sample hit

• mem: location in memory or other places the sample hit

• dtlb: location in Data TLB (L1, L2) where the sample hit

• snoop: snoop result for the sampled data access

Please take a look at the OUTPUT FIELD SELECTION section for caveats.

-T, --type-profile
Show data-type profile result instead of code symbols. This requires the debug information and it
will change the default sort keys to: mem, snoop, tlb, type.

-U, --hide-unresolved
Only display entries resolved to a symbol.

-x, --field-separator=<separator>
Specify the field separator used when dump raw samples (-D option). By default, The separator is the
space character.

In addition, for report all perf report options are valid, and for record all perf record options.

OVERHEAD CALCULATION

       Unlike perf-report(1), which calculates overhead from the actual sample period, perf-mem overhead is
       calculated using sample weight. E.g. there are two samples in perf.data file, both with the same sample
       period, but one sample with weight 180 and the other with weight 20:

           $ perf script -F period,data_src,weight,ip,sym
           100000    629080842 |OP LOAD|LVL L3 hit|...     20       7e69b93ca524 strcmp
           100000   1a29081042 |OP LOAD|LVL RAM hit|...   180   ffffffff82429168 memcpy

           $ perf report -F overhead,symbol
           50%   [.] strcmp
           50%   [k] memcpy

           $ perf mem report -F overhead,symbol
           90%   [k] memcpy
           10%   [.] strcmp

OUTPUT FIELD SELECTION

"perf mem report" adds a number of new output fields specific to data source information in the sample.
Some of them have the same name with the existing sort keys ("mem" and "snoop"). So unlike other fields
and sort keys, they’ll behave differently when it’s used by -F/--fields or -s/--sort.

Using those two as output fields will aggregate samples altogether and show breakdown.

$ perf mem report -F mem,snoop
...
# ------ Memory ------- --- Snoop ----
# RAM Uncach Other HitM Other
# ..................... ..............
#
3.5% 0.0% 96.5% 25.1% 74.9%

But using the same name for sort keys will aggregate samples for each type separately.

$ perf mem report -s mem,snoop
# Overhead Samples Memory access Snoop
# ........ ............ ....................................... ............
#
47.99% 1509 L2 hit N/A
25.08% 338 core, same node Any cache hit HitM
10.24% 54374 N/A N/A
6.77% 35938 L1 hit N/A
6.39% 101 core, same node Any cache hit N/A
3.50% 69 RAM hit N/A
0.03% 158 LFB/MAB hit N/A
0.00% 2 Uncached hit N/A