[PATCH v2] new: Don't scan unchanged directories with no sub-directories

[David Bremner]

David Bremner <david at tethera.net> writes:

> Austin Clements <amdragon at MIT.EDU> writes:
>
>> This can substantially reduce the cost of notmuch new in some
>> situations, such as when the file system cache is cold or when the
>> Maildir is on NFS.
>
> On my desktop at home (a core i7 950) with spinning rust disks (and lvm
> on luks) this patch yields about a 7% slowdown in the intial new perf
> test
>
> from
>
> 			Wall(s)	Usr(s)	Sys(s)	Res(K)	In/Out(512B)
>   Initial notmuch new   579.60	348.86	14.26	217188	5330266/3501272
>
> to
>
> 			Wall(s)	Usr(s)	Sys(s)	Res(K)	In/Out(512B)
>   Initial notmuch new   620.51	368.62	15.48	217156	5330354/3416456
>
> On an SSD I don't detect a significant different (<0.5% speedup)

Seems like a false alarm. Averaging over 10 repetitions, the patched
version is about 1% faster. Unfortunately it points out that our
performance test suite should really do more than one repetition for
each test.

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