[M] Change in osmocom-bb[master]: trx_toolkit/*: Try to avoid copying burst data where possible - gerrit-log

13 Feb 2025

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kirr has posted comments on this change by kirr. (
https://gerrit.osmocom.org/c/osmocom-bb/+/39537?usp=email )

Change subject: trx_toolkit/*: Try to avoid copying burst data where possible
......................................................................

Patch Set 2:

(1 comment)

File src/target/trx_toolkit/data_msg.py:

https://gerrit.osmocom.org/c/osmocom-bb/+/39537/comment/7ef9a2d0_e46bcac8?u… :
PS2, Line 336: 				burst = memoryview(burst)[:EDGE_BURST_LEN]
...
  I never used memoryview nor read about the details,
but in line "burst = memoryview(burst)[:EDGE_BUR […] ah, now I see. So
memoryview(burst) creates only a view of original burst object data. This is basically a
small object that points to another base object to know where to get the data without
copying them. Then slice operation of memoryview returns another memoryview without
copying the data - that adjusted memoryview refers to base object, but knows to view not
the whole data of it, but only some range. It is still a small object that does not copy
base's data.

```
In [7]: burst = bytearray(range(10))                                                      

In [8]: burst                                                                             

Out[8]: bytearray(b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t')                      

In [9]: burst *= 100

In [10]: burst
Out[10]:
bytearray(b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t...\x00\x01\x02\x03\x04\x05\x06\x07\x08\t')

In [11]: len(burst)
Out[11]: 1000

In [12]: sys.getsizeof(burst)
Out[12]: 1057

In [13]: m = memoryview(burst)

In [14]: len(m)
Out[14]: 1000

In [15]: sys.getsizeof(m)
Out[15]: 184

In [16]: m[0]
Out[16]: 0

In [17]: burst[0]
Out[17]: 0

In [18]: burst[1]
Out[18]: 1

In [19]: m[1]
Out[19]: 1

In [20]: m[2]
Out[20]: 2

In [21]: burst[2]
Out[21]: 2

In [22]: mm = m[2:]

In [23]: len(mm)
Out[23]: 998

In [24]: sys.getsizeof(mm)
Out[24]: 184

In [25]: mm[0]
Out[25]: 2

In [26]: m[2]
Out[26]: 2

In [27]: mm[1]
Out[27]: 3

In [28]: m[3]
Out[28]: 3

In [29]: burst[3]
Out[29]: 3
```

Please see https://docs.python.org/3/library/stdtypes.html#memoryview for details.

P.S. Unfortunately constant-size of memoryview structure turned out to be not so small, so
it still contributes to overhead for not so small bursts.
https://github.com/python/cpython/blob/v3.11.9-9-g1b0e63c81b5/Include/memor…

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Gerrit-Project: osmocom-bb
Gerrit-Branch: master
Gerrit-Change-Id: I147da2f110dedc863361059c931f609c28a69e9c
Gerrit-Change-Number: 39537
Gerrit-PatchSet: 2
Gerrit-Owner: kirr &lt;kirr(a)nexedi.com&gt;
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Gerrit-Reviewer: pespin &lt;pespin(a)sysmocom.de&gt;
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