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NAME | SYNOPSIS | DESCRIPTION | RECORD OPTIONS | REPORT OPTIONS | C2C RECORD | C2C REPORT | NODE INFO | COALESCE | STDIO OUTPUT | TUI OUTPUT | CREDITS | C2C BLOG | SEE ALSO | COLOPHON |
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PERF-C2C(1) perf Manual PERF-C2C(1)
perf-c2c - Shared Data C2C/HITM Analyzer.
perf c2c record [<options>] <command>
perf c2c record [<options>] -- [<record command options>] <command>
perf c2c report [<options>]
C2C stands for Cache To Cache.
The perf c2c tool provides means for Shared Data C2C/HITM
analysis. It allows you to track down the cacheline contentions.
On Intel, the tool is based on load latency and precise store
facility events provided by Intel CPUs. On PowerPC, the tool uses
random instruction sampling with thresholding feature. On AMD,
the tool uses IBS op pmu (due to hardware limitations, perf c2c
is not supported on Zen3 cpus). On Arm64 it 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 Arm SPE sampling, not every memory
operation will be sampled.
These events provide: - memory address of the access - type of
the access (load and store details) - latency (in cycles) of the
load access
The c2c tool provide means to record this data and report back
access details for cachelines with highest contention - highest
number of HITM accesses.
The basic workflow with this tool follows the standard
record/report phase. User uses the record command to record
events data and report command to display it.
-e, --event=
Select the PMU event. Use perf c2c record -e list to list
available events.
-v, --verbose
Be more verbose (show counter open errors, etc).
-l, --ldlat
Configure mem-loads latency. Supported on Intel and Arm64
processors only. Ignored on other archs.
-k, --all-kernel
Configure all used events to run in kernel space.
-u, --all-user
Configure all used events to run in user space.
-k, --vmlinux=<file>
vmlinux pathname
-v, --verbose
Be more verbose (show counter open errors, etc).
-i, --input
Specify the input file to process.
-N, --node-info
Show extra node info in report (see NODE INFO section)
-c, --coalesce
Specify sorting fields for single cacheline display.
Following fields are available: tid,pid,iaddr,dso (see
COALESCE)
-g, --call-graph
Setup callchains parameters. Please refer to perf-report man
page for details.
--stdio
Force the stdio output (see STDIO OUTPUT)
--stats
Display only statistic tables and force stdio mode.
--full-symbols
Display full length of symbols.
--no-source
Do not display Source:Line column.
--show-all
Show all captured HITM lines, with no regard to HITM % 0.0005
limit.
-f, --force
Don’t do ownership validation.
-d, --display
Switch to HITM type (rmt, lcl) or peer snooping type (peer)
to display and sort on. Total HITMs (tot) as default, except
Arm64 uses peer mode as default.
--stitch-lbr
Show callgraph with stitched LBRs, which may have more
complete callgraph. The perf.data file must have been
obtained using perf c2c record --call-graph lbr. Disabled by
default. In common cases with call stack overflows, it can
recreate better call stacks than the default lbr call stack
output. But this approach is not foolproof. There can be
cases where it creates incorrect call stacks from incorrect
matches. The known limitations include exception handing such
as setjmp/longjmp will have calls/returns not match.
--double-cl
Group the detection of shared cacheline events into double
cacheline granularity. Some architectures have an Adjacent
Cacheline Prefetch feature, which causes cacheline sharing to
behave like the cacheline size is doubled.
The perf c2c record command setup options related to HITM
cacheline analysis and calls standard perf record command.
Following perf record options are configured by default: (check
perf record man page for details)
-W,-d,--phys-data,--sample-cpu
Unless specified otherwise with -e option, following events are
monitored by default on Intel:
cpu/mem-loads,ldlat=30/P
cpu/mem-stores/P
following on AMD:
ibs_op//
and following on PowerPC:
cpu/mem-loads/
cpu/mem-stores/
User can pass any perf record option behind -- mark, like (to
enable callchains and system wide monitoring):
$ perf c2c record -- -g -a
Please check RECORD OPTIONS section for specific c2c record
options.
The perf c2c report command displays shared data analysis. It
comes in two display modes: stdio and tui (default).
The report command workflow is following: - sort all the data
based on the cacheline address - store access details for each
cacheline - sort all cachelines based on user settings - display
data
In general perf report output consist of 2 basic views: 1) most
expensive cachelines list 2) offsets details for each cacheline
For each cacheline in the 1) list we display following data:
(Both stdio and TUI modes follow the same fields output)
Index
- zero based index to identify the cacheline
Cacheline
- cacheline address (hex number)
Rmt/Lcl Hitm (Display with HITM types)
- cacheline percentage of all Remote/Local HITM accesses
Peer Snoop (Display with peer type)
- cacheline percentage of all peer accesses
LLC Load Hitm - Total, LclHitm, RmtHitm (For display with HITM types)
- count of Total/Local/Remote load HITMs
Load Peer - Total, Local, Remote (For display with peer type)
- count of Total/Local/Remote load from peer cache or DRAM
Total records
- sum of all cachelines accesses
Total loads
- sum of all load accesses
Total stores
- sum of all store accesses
Store Reference - L1Hit, L1Miss, N/A
L1Hit - store accesses that hit L1
L1Miss - store accesses that missed L1
N/A - store accesses with memory level is not available
Core Load Hit - FB, L1, L2
- count of load hits in FB (Fill Buffer), L1 and L2 cache
LLC Load Hit - LlcHit, LclHitm
- count of LLC load accesses, includes LLC hits and LLC HITMs
RMT Load Hit - RmtHit, RmtHitm
- count of remote load accesses, includes remote hits and remote HITMs;
on Arm neoverse cores, RmtHit is used to account remote accesses,
includes remote DRAM or any upward cache level in remote node
Load Dram - Lcl, Rmt
- count of local and remote DRAM accesses
For each offset in the 2) list we display following data:
HITM - Rmt, Lcl (Display with HITM types)
- % of Remote/Local HITM accesses for given offset within cacheline
Peer Snoop - Rmt, Lcl (Display with peer type)
- % of Remote/Local peer accesses for given offset within cacheline
Store Refs - L1 Hit, L1 Miss, N/A
- % of store accesses that hit L1, missed L1 and N/A (no available) memory
level for given offset within cacheline
Data address - Offset
- offset address
Pid
- pid of the process responsible for the accesses
Tid
- tid of the process responsible for the accesses
Code address
- code address responsible for the accesses
cycles - rmt hitm, lcl hitm, load (Display with HITM types)
- sum of cycles for given accesses - Remote/Local HITM and generic load
cycles - rmt peer, lcl peer, load (Display with peer type)
- sum of cycles for given accesses - Remote/Local peer load and generic load
cpu cnt
- number of cpus that participated on the access
Symbol
- code symbol related to the 'Code address' value
Shared Object
- shared object name related to the 'Code address' value
Source:Line
- source information related to the 'Code address' value
Node
- nodes participating on the access (see NODE INFO section)
The Node field displays nodes that accesses given cacheline
offset. Its output comes in 3 flavors: - node IDs separated by ,
- node IDs with stats for each ID, in following format: Node{cpus
%hitms %stores} (Display with HITM types) Node{cpus %peers
%stores} (Display with peer type) - node IDs with list of
affected CPUs in following format: Node{cpu list}
User can switch between above flavors with -N option or use n key
to interactively switch in TUI mode.
User can specify how to sort offsets for cacheline.
Following fields are available and governs the final output
fields set for cacheline offsets output:
tid - coalesced by process TIDs
pid - coalesced by process PIDs
iaddr - coalesced by code address, following fields are displayed:
Code address, Code symbol, Shared Object, Source line
dso - coalesced by shared object
By default the coalescing is setup with pid,iaddr.
The stdio output displays data on standard output.
Following tables are displayed: Trace Event Information - overall
statistics of memory accesses
Global Shared Cache Line Event Information
- overall statistics on shared cachelines
Shared Data Cache Line Table
- list of most expensive cachelines
Shared Cache Line Distribution Pareto
- list of all accessed offsets for each cacheline
The TUI output provides interactive interface to navigate through
cachelines list and to display offset details.
For details please refer to the help window by pressing ? key.
Although Don Zickus, Dick Fowles and Joe Mario worked together to
get this implemented, we got lots of early help from Arnaldo
Carvalho de Melo, Stephane Eranian, Jiri Olsa and Andi Kleen.
Check Joe’s blog on c2c tool for detailed use case explanation:
https://joemario.github.io/blog/2016/09/01/c2c-blog/
perf-record(1), perf-mem(1), perf-arm-spe(1)
This page is part of the perf (Performance analysis tools for
Linux (in Linux source tree)) project. Information about the
project can be found at
⟨https://perf.wiki.kernel.org/index.php/Main_Page⟩. If you have a
bug report for this manual page, send it to
[email protected]. This page was obtained from the
project's upstream Git repository
⟨http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git⟩
on 2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-13.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
perf 2023-02-16 PERF-C2C(1)
Pages that refer to this page: perf(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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