Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4

From: Yang Jihong
Date: Fri May 05 2023 - 21:13:49 EST

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Hello,

On 2023/5/5 21:18, Arnaldo Carvalho de Melo wrote:

Em Thu, May 04, 2023 at 07:01:51PM -0300, Arnaldo Carvalho de Melo escreveu:

Em Thu, May 04, 2023 at 06:48:50PM -0300, Arnaldo Carvalho de Melo escreveu:

Em Thu, May 04, 2023 at 04:07:29PM -0300, Arnaldo Carvalho de Melo escreveu:

Em Thu, May 04, 2023 at 11:50:07AM -0700, Andrii Nakryiko escreveu:

On Thu, May 4, 2023 at 10:52 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:

Andrii, can you add some more information about the usage of vmlinux.h
instead of using kernel headers?

I'll just say that vmlinux.h is not a hard requirement to build BPF
programs, it's more a convenience allowing easy access to definitions
of both UAPI and kernel-internal structures for tracing needs and
marking them relocatable using BPF CO-RE machinery. Lots of real-world
applications just check-in pregenerated vmlinux.h to avoid build-time
dependency on up-to-date host kernel and such.

If vmlinux.h generation and usage is causing issues, though, given
that perf's BPF programs don't seem to be using many different kernel
types, it might be a better option to just use UAPI headers for public
kernel type definitions, and just define CO-RE-relocatable minimal
definitions locally in perf's BPF code for the other types necessary.
E.g., if perf needs only pid and tgid from task_struct, this would
suffice:

struct task_struct {
int pid;
int tgid;
} __attribute__((preserve_access_index));

Yeah, that seems like a way better approach, no vmlinux involved, libbpf
CO-RE notices that task_struct changed from this two integers version
(of course) and does the relocation to where it is in the running kernel
by using /sys/kernel/btf/vmlinux.

Doing it for one of the skels, build tested, runtime untested, but not
using any vmlinux, BTF to help, not that bad, more verbose, but at least
we state what are the fields we actually use, have those attribute
documenting that those offsets will be recorded for future use, etc.

Yang, can you please check that this works?

Yes, I've tested this patch and it works :)

Tested-by: Yang Jihong <yangjihong1@xxxxxxxxxx>

# perf kwork report -b
Starting trace, Hit <Ctrl+C> to stop and report
^C
Kwork Name | Cpu | Total Runtime | Count | Max runtime | Max runtime start | Max runtime end |

--------------------------------------------------------------------------------------------------------------------------------
(s)SCHED:7 | 0005 | 1.440 ms | 3 | 1.377 ms | 165822.963188 s | 165822.964565 s |
(s)SCHED:7 | 0001 | 1.388 ms | 2 | 1.377 ms | 165822.963188 s | 165822.964565 s |
(w)e1000_watchdog | 0002 | 0.532 ms | 1 | 0.532 ms | 165823.806777 s | 165823.807309 s |
(w)flush_to_ldisc | 0005 | 0.524 ms | 1 | 0.524 ms | 165824.255219 s | 165824.255743 s |
(s)NET_RX:3 | 0002 | 0.512 ms | 4 | 0.247 ms | 165824.254103 s | 165824.254350 s |
(w)wq_barrier_func | 0003 | 0.394 ms | 1 | 0.394 ms | 165822.964179 s | 165822.964573 s |
eth0:10 | 0002 | 0.250 ms | 4 | 0.115 ms | 165822.964814 s | 165822.964929 s |
(w)wb_workfn | 0005 | 0.208 ms | 1 | 0.208 ms | 165823.998558 s | 165823.998766 s |
(s)TIMER:1 | 0002 | 0.205 ms | 4 | 0.077 ms | 165823.806548 s | 165823.806626 s |
(s)SCHED:7 | 0002 | 0.185 ms | 5 | 0.049 ms | 165824.255119 s | 165824.255168 s |
(s)TIMER:1 | 0003 | 0.167 ms | 4 | 0.079 ms | 165823.998326 s | 165823.998405 s |
(s)SCHED:7 | 0000 | 0.165 ms | 4 | 0.073 ms | 165823.807235 s | 165823.807308 s |
(w)flush_to_ldisc | 0003 | 0.156 ms | 1 | 0.156 ms | 165824.255723 s | 165824.255879 s |
(s)TIMER:1 | 0007 | 0.152 ms | 2 | 0.100 ms | 165823.358416 s | 165823.358517 s |
(w)vmstat_update | 0001 | 0.094 ms | 1 | 0.094 ms | 165824.256460 s | 165824.256554 s |
(s)RCU:9 | 0001 | 0.088 ms | 4 | 0.040 ms | 165822.964728 s | 165822.964768 s |
(w)vmstat_shepherd | 0000 | 0.078 ms | 1 | 0.078 ms | 165824.256321 s | 165824.256399 s |
(s)SCHED:7 | 0007 | 0.066 ms | 2 | 0.038 ms | 165823.358528 s | 165823.358566 s |
(s)SCHED:7 | 0003 | 0.057 ms | 2 | 0.034 ms | 165823.998412 s | 165823.998446 s |
virtio0-requests:25 | 0000 | 0.056 ms | 1 | 0.056 ms | 165824.255959 s | 165824.256016 s |
(s)TIMER:1 | 0000 | 0.055 ms | 1 | 0.055 ms | 165824.256164 s | 165824.256219 s |
(s)RCU:9 | 0005 | 0.045 ms | 3 | 0.023 ms | 165822.964728 s | 165822.964751 s |
(s)RCU:9 | 0002 | 0.028 ms | 2 | 0.017 ms | 165823.174539 s | 165823.174556 s |
(s)RCU:9 | 0007 | 0.016 ms | 1 | 0.016 ms | 165823.358571 s | 165823.358587 s |
(s)RCU:9 | 0000 | 0.013 ms | 1 | 0.013 ms | 165824.256264 s | 165824.256278 s |
(s)RCU:9 | 0003 | 0.011 ms | 1 | 0.011 ms | 165822.973142 s | 165822.973153 s |

--------------------------------------------------------------------------------------------------------------------------------

# perf kwork lat -b
Starting trace, Hit <Ctrl+C> to stop and report
^C
Kwork Name | Cpu | Avg delay | Count | Max delay | Max delay start | Max delay end |

--------------------------------------------------------------------------------------------------------------------------------
(w)neigh_periodic_work | 0001 | 0.568 ms | 1 | 0.568 ms | 165839.038372 s | 165839.038941 s |
(s)RCU:9 | 0000 | 0.292 ms | 1 | 0.292 ms | 165840.176224 s | 165840.176515 s |
(s)TIMER:1 | 0000 | 0.260 ms | 1 | 0.260 ms | 165840.176206 s | 165840.176466 s |
(w)disk_events_workfn | 0001 | 0.256 ms | 1 | 0.256 ms | 165839.038327 s | 165839.038583 s |
(s)RCU:9 | 0001 | 0.204 ms | 1 | 0.204 ms | 165839.038213 s | 165839.038417 s |
(s)SCHED:7 | 0001 | 0.153 ms | 1 | 0.153 ms | 165839.038231 s | 165839.038384 s |
(s)NET_RX:3 | 0002 | 0.132 ms | 3 | 0.184 ms | 165840.175984 s | 165840.176168 s |
(w)ata_sff_pio_task | 0001 | 0.124 ms | 1 | 0.124 ms | 165839.038852 s | 165839.038976 s |
(s)SCHED:7 | 0000 | 0.122 ms | 2 | 0.193 ms | 165840.176244 s | 165840.176437 s |
(s)RCU:9 | 0007 | 0.106 ms | 1 | 0.106 ms | 165838.982220 s | 165838.982326 s |
(s)RCU:9 | 0003 | 0.092 ms | 1 | 0.092 ms | 165839.040098 s | 165839.040189 s |
(s)TIMER:1 | 0001 | 0.085 ms | 1 | 0.085 ms | 165839.038179 s | 165839.038264 s |
(s)SCHED:7 | 0007 | 0.078 ms | 3 | 0.086 ms | 165839.990180 s | 165839.990265 s |
(s)TIMER:1 | 0007 | 0.077 ms | 3 | 0.081 ms | 165839.990136 s | 165839.990216 s |
(s)TIMER:1 | 0003 | 0.076 ms | 1 | 0.076 ms | 165839.040066 s | 165839.040142 s |
(s)RCU:9 | 0002 | 0.075 ms | 2 | 0.088 ms | 165839.118209 s | 165839.118297 s |
(w)flush_to_ldisc | 0006 | 0.070 ms | 1 | 0.070 ms | 165840.175332 s | 165840.175402 s |
(s)TIMER:1 | 0006 | 0.067 ms | 2 | 0.085 ms | 165838.908056 s | 165838.908142 s |
(s)TIMER:1 | 0002 | 0.067 ms | 2 | 0.074 ms | 165840.175076 s | 165840.175149 s |
(s)SCHED:7 | 0006 | 0.065 ms | 1 | 0.065 ms | 165838.908107 s | 165838.908171 s |
(s)SCHED:7 | 0003 | 0.051 ms | 1 | 0.051 ms | 165839.040115 s | 165839.040166 s |
(s)SCHED:7 | 0002 | 0.046 ms | 2 | 0.048 ms | 165840.175123 s | 165840.175171 s |
(s)RCU:9 | 0006 | 0.035 ms | 2 | 0.036 ms | 165838.913051 s | 165838.913087 s |
(s)BLOCK:4 | 0001 | 0.023 ms | 1 | 0.023 ms | 165839.039281 s | 165839.039303 s |

--------------------------------------------------------------------------------------------------------------------------------

Thanks,
Yang

Next message: Huang, Ying: "Re: [RFC PATCH 4/4] llist.h: Fix parentheses around macro pointer parameter use"
Previous message: Adam Ford: "[PATCH V4 6/6] drm: bridge: samsung-dsim: Support non-burst mode"
In reply to: Arnaldo Carvalho de Melo: "Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4"
Next in thread: Arnaldo Carvalho de Melo: "Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4"
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