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Message-ID: <20130519205120.GF20323@brightrain.aerifal.cx>
Date: Sun, 19 May 2013 16:51:20 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: cpuset/affinity interfaces and TSX lock elision in musl
On Sat, May 18, 2013 at 11:40:32PM -0500, Rob Landley wrote:
> On 05/17/2013 12:29:03 PM, Rich Felker wrote:
> >> locks should not be the bottleneck in applications
> >> unless there is too much shared state on hot paths,
> >> which is probably a design bug or a special use-case
> >> for which non-standard synchronization methods may
> >> be better anyway
> >
> >One place where there is unfortunately a huge amount of shared state
> >is memory management; this is inevitable. Even if we don't use lock
> >elision for pthread locks, it might be worth considering using it
> >_internally_ in malloc when it's available. It's hard to say without
> >any measurements, but this might result in a malloc that beats
> >ptmalloc, etc. without any thread-locale management.
>
> I thought the point of futexes was that in the non-contention case
> you don't enter the kernel at all?
>
> I really don't see how lock elision is supposed to improve upon
> that. If you're optimizing the contended case, something is wrong.
Yes, that "something" is C++ (and by extension, glib, which might as
well be C++ but worse). But we're not in a position to fix it.
Rich
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