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Re: [PATCH 02/11] libports: use a single hash table
From: |
Samuel Thibault |
Subject: |
Re: [PATCH 02/11] libports: use a single hash table |
Date: |
Tue, 13 May 2014 12:53:59 +0200 |
User-agent: |
Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30) |
Justus Winter, le Tue 13 May 2014 12:48:46 +0200, a écrit :
> Quoting Samuel Thibault (2014-05-13 01:00:30)
> > Justus Winter, le Mon 12 May 2014 12:05:40 +0200, a écrit :
> > > Previously, libports used a hash table per port bucket. This makes
> > > looking up a port difficult if one does not know the port bucket, as
> > > one has to iterate over all buckets and do a hash table lookup each.
> >
> > But conversely, this makes having to iterate over all ports while one
> > may want to just iterate over one bucket. I'd rather not drop that
> > feature.
>
> This feature is not lost. ports_bucket_iterate (b, ..) iterates over
> all ports in bucket b as before.
But not in an efficient way, it'll iterate over the whole global
hashtable, not only the per-bucket hash table.
> Also, looking up a port is often done. Iterating over the ports is
> done much less often. It seems to me that optimizing the former is
> more important.
>
> > _ports_bucket_class_iterate is clearly bogus ATM, so we at least need
> > something. Would it be too costly to maintain both a global and a
> > per-bucket hash table? It would at the very worse be only twice as
> > expensive as only the global hash table, while still allowing the
> > performance gain of iterating over only one bucket.
>
> Having more than one hash table is totally pointless imho. Since the
> port namespace is per-process, and libports is "per-process", having a
> hash table per bucket means that all per-bucket hash tables are
> disjoint.
Well, yes, indeed, of course. But that's my whole point: keeping the
per-bucket hash table too allows to iterate over a bucket efficiently.
Samuel
[PATCH 06/11] libtrivfs: lock-less reference counting for trivfs_peropen objects, Justus Winter, 2014/05/12
[PATCH 02/11] libports: use a single hash table, Justus Winter, 2014/05/12
[PATCH 04/11] libports: lock-less reference counting for port_info objects, Justus Winter, 2014/05/12
[PATCH 08/11] libihash: reduce the default maximum load factor to 75%, Justus Winter, 2014/05/12
[PATCH 11/11] fatfs: improve {enable,disable}_caching, Justus Winter, 2014/05/12