id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
1954809370,I_kwDOAMm_X850hAYa,8353,Update benchmark suite for asv 0.6.1,2448579,open,0,,,0,2023-10-20T18:13:22Z,2023-12-19T05:53:21Z,,MEMBER,,,,"The new asv version comes with decorators for parameterizing and skipping, and the ability to use `mamba` to create environments.

https://github.com/airspeed-velocity/asv/releases

https://asv.readthedocs.io/en/v0.6.1/writing_benchmarks.html#skipping-benchmarks

This might help us reduce benchmark times a bit, or at least simplify the code some.
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1954445639,I_kwDOAMm_X850fnlH,8350,optimize align for scalars at least,2448579,open,0,,,5,2023-10-20T14:48:25Z,2023-10-20T19:17:39Z,,MEMBER,,,,"### What happened?

Here's a simple rescaling calculation:
```python
import numpy as np
import xarray as xr

ds = xr.Dataset(
    {""a"": ((""x"", ""y""), np.ones((300, 400))), ""b"": ((""x"", ""y""), np.ones((300, 400)))}
)
mean = ds.mean() # scalar
std = ds.std() # scalar
rescaled = (ds - mean) / std
```

The profile for the last line shows 30% (!!!) time spent in `align` (really `reindex_like`) except there's nothing to reindex when only scalars are involved! 

<img width=""1088"" alt=""image"" src=""https://github.com/pydata/xarray/assets/2448579/426de01a-e05c-46cf-9f86-25333b4843be"">

This is a small example inspired by a ML pipeline where this normalization is happening very many times in a tight loop.

cc @benbovy 

### What did you expect to happen?

A fast path for when no reindexing needs to happen.
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1954535213,PR_kwDOAMm_X85dZT47,8351,"[skip-ci] Add benchmarks for Dataset binary ops, chunk",2448579,closed,0,,,1,2023-10-20T15:31:36Z,2023-10-20T18:08:40Z,2023-10-20T18:08:38Z,MEMBER,,0,pydata/xarray/pulls/8351,"xref #8339
xref #8350
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1954360112,PR_kwDOAMm_X85dYtpz,8349,[skip-ci] dev whats-new,2448579,closed,0,,,1,2023-10-20T14:02:07Z,2023-10-20T17:28:19Z,2023-10-20T14:54:30Z,MEMBER,,0,pydata/xarray/pulls/8349,"<!-- Feel free to remove check-list items aren't relevant to your change -->

- [ ] Closes #xxxx
- [ ] Tests added
- [ ] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
- [ ] New functions/methods are listed in `api.rst`
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