Delete the element from the starts map after it has been used.
#5416
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I think it has been an omission, as opposed to an optimization, in the
original change that introduced this. The python version of the
`funclatency` has the delete after the lookup.
Before the change:
./funclatency nvme_setup_cmd
Tracing nvme_setup_cmd. Hit Ctrl-C to exit
^C
nsec : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 243 |****************************************|
1024 -> 2047 : 43 |******* |
2048 -> 4095 : 59 |********* |
4096 -> 8191 : 26 |**** |
After the change:
./funclatency nvme_setup_cmd
Tracing nvme_setup_cmd. Hit Ctrl-C to exit
^C
nsec : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 4 | |
512 -> 1023 : 624 |****************************************|
1024 -> 2047 : 39 |** |
2048 -> 4095 : 98 |****** |
4096 -> 8191 : 71 |**** |
8192 -> 16383 : 1 | |
mogoreanu
requested review from
brendangregg,
chenhengqi,
ekyooo and
yonghong-song
as code owners
chenhengqi
reviewed
Oct 30, 2025
libbpf-tools/funclatency.bpf.c
Outdated
| start = bpf_map_lookup_elem(&starts, &pid); | ||
| if (!start) | ||
| return; | ||
| bpf_map_delete_elem(&starts, &pid); |
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This cleanup should be done at the end of this function.
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I think it has been an omission, as opposed to an optimization, in the original change that introduced this. The python version of the
funclatencyhas the delete after the lookup.Before the change:
./funclatency nvme_setup_cmd
Tracing nvme_setup_cmd. Hit Ctrl-C to exit
^C
nsec : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 243 |********************|
1024 -> 2047 : 43 | |
2048 -> 4095 : 59 | |
4096 -> 8191 : 26 | |
After the change:
./funclatency nvme_setup_cmd
Tracing nvme_setup_cmd. Hit Ctrl-C to exit
^C
nsec : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 4 | |
512 -> 1023 : 624 |******************************|
1024 -> 2047 : 39 |** |
2048 -> 4095 : 98 | |
4096 -> 8191 : 71 | |
8192 -> 16383 : 1 | |