On Mon, Jan 30, 2012, David Chisnall wrote:
> On 18 Jan 2012, at 19:07, David Schultz wrote:
>
> > This patch appears to cause a large performance regression. For
> > example, I measured a 78% slowdown for strtol(" 42", ...).
>
> That's definitely worth taking a closer look at. I think we can cache some
> things in TLS and avoid some pthread_getspecific calls. The current code is
> the 'make it work' version. The 'make it fast' version is planned...
Sounds good; I look forward to it.
> > Furthermore, the resulting static binary for a trivial program
> > goes from 7k to 303k, due to pulling in malloc, stdio, and all the
> > pthread stubs.
>
> That's not ideal, but I'm not sure if it's avoidable. Is statically linking
> libc something people regularly do?
Aside from bde, probably not many. This is definitely a
second-order concern.
FreeBSD has a set of statically linked binaries in /rescue for
situations where /lib gets screwed up. Space is an issue there
because the root partition is historically sized quite small.
Embedded folks might also care, but I'll let them speak for
themselves. I did get a request several years ago from an
embedded developer to unbreak the NO_FLOATING_POINT option in
libc, and you could imagine perhaps a NO_LOCALE option as well.
> Yup. A quick-and-dirty hack would be to add a flag that was set on the first
> call to uselocale() and to always use the global locale if this is not set.
> That should remove a lot of the overhead in cases where no one uses the
> per-thread locales.
>
> We can also probably store the locale in TLS, which (on platforms with fast
> TLS) should speed up the lookup a bit.
I thought that's what thread_(get|set)_locale already did.
Actually, it's counterintuitive that it would be significantly
slower to access per-thread state than global state. Any idea
why? Maybe it says something about our pthread_getspecific()
implementation. I will run the code through a profiler some
day, but I don't have the cycles right now.
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