Re: zero-alloc cache (was Re: [v3] Fix PR libstdc++/10276)

["B. Kosnik" <bkoz at nabi dot net>]

>I See I am too late for 3.3.0 :-(  Unfortunately, I haven't had the
>bandwidth to sort this out fast enough for the release.  So my
>apologies for ending up on the critical path.

No worries. Now we are free to work it out without the pressure of
looming deadlines.

>Yeah, that's very disappointing.  With v3 as I just checked it out,
>3.3 is still more than 2X slower than 2.95 on writing ints to file.
>But we're making forward progress.

Yep.

> > I'm also having second thoughts about this approach to locale caching in
> > general. I've implemented __has_cache/__use_cache and while it's not as fast
> > as the __locale_cache code as present, it's still on par with 2.95 and
> > it seems like a better way to go.
> > 
> > Awful lot of "I's" in the above text. Your honest feedback is appreciated.
>
>I'd rather see it in there than not.  For sure, the ABI compatibility
>puts some limitations on what we can do.  And I agree that the pword
>method has some unpleasant aspects to it.  Also, we need something
>like the __has_cache approach to deal with the problem pointed out by
>Petur in this thread:
>http://gcc.gnu.org/ml/libstdc++/2003-04/msg00023.html

Yeah.

>Will the __has_cache approach be ABI compatible and avoid the
>allocation issues that are sinking the current approach?
>
>I remember suggesting that the pword mechanism might be used to hold
>this stuff if ABI concerns pop up again.  Although this will again
>require fiddling with the static streams.

Uncertain. I liked the pword mechanism for fitting this stuff back into
3.2.x abi, actually. It seems to work pretty well.

>I'd like to see the patch.  I'm surprised you are getting speeds
>equivalent to 2.95.

I've gotten better results with mainline than v2 for a while now. This
is on athlon/p4/p3.

I'll try to clean it up enough to post. Some critical bits remain
unresolved, and I just hacked through all the ctype issues instead of
dealing with them correctly. I was just looking at num_put.

RH9, T30 (P4/1.8G/512) 2.96
6.630u 0.420s 0:09.40 75.0%     0+0k 0+0io 137pf+0w

RH9, T30 (P4/1.8G/512) 20030429-gcc-sh.exe
5.880u 0.410s 0:09.83 63.9%     0+0k 0+0io 215pf+0w

RH9, T30 (P4/1.8G/512) 20030429-gcc-static.exe NO __locale_cache
12.610u 0.390s 0:18.70 69.5%    0+0k 0+0io 122pf+0w

RH9, T30 (P4/1.8G/512) 20030429-gcc-3_3-branch.exe __use_cache
7.000u 0.300s 0:07.67 95.1%     0+0k 0+0io 124pf+0w


>I thought I mostly had (once I was aware of it), but I'll be more
>explicit and careful about it in the future.

Yep. I fixed up 'check-abi' for both added symbols and missing symbols.

-benjamin