[Mono-dev] [PATCH] - optimization for System.Xml.XmlNode::SelectSingleNode

[tom hindle]

On Mon, 2010-05-10 at 19:28 +0100, Alan McGovern wrote:
> Why would a c-cast be so much slower than an 'as' cast? Surely they
> should be equivalent or the c-cast should be faster.

sorry bad terminology...

I meant syntactically c-style cast not an actual c-cast. I wasn't sure
the C# name for it, maybe it called a prefix cast?

Tom

> 
> Alan.
> 
> On Mon, May 10, 2010 at 7:24 PM, Atsushi Eno
> <atsushieno at veritas-vos-liberabit.com> wrote:
> > Well, it wasn't really internal, but that does not affect my statement.
> >
> > Atsushi Eno
> >
> > On 2010/05/11 2:55, Atsushi Eno wrote:
> >> Hi,
> >>
> >> Thanks Tom, it looks like a good catch. The interface is internal, and
> >> cast exceptions should not happen there anyways. Once the build got
> >> fixed, I'll verify the patch and apply it unless it regresses.
> >>
> >> Atsushi Eno
> >>
> >>
> >> On 2010/05/11 2:09, tom hindle wrote:
> >>
> >>> Hi,
> >>>
> >>> While performance profiling our code, with mono's nice profiling
> >>> tools :), I noticed System.Xml.XmlNode::SelectSingleNode was taking 23ms
> >>> a call while the sum of the methods it was calling took<   5ms.
> >>> SelectSingleNode is a very simple method however it contains a (dynamic)
> >>> down cast. I replaced the (Cstyle/prefix) cast with a 'as' cast and this
> >>> seem to reduce the method time by about 7ms.
> >>>
> >>>
> >>> // With 'Cstyle' cast
> >>>    39672.303    1717   23.106
> >>> System.Xml.XmlNode::SelectSingleNode(string,XmlNamespaceManager)
> >>>     Callers (with count) that contribute at least for 1%:
> >>>           1717  100 % System.Xml.XmlNode::SelectSingleNode(string)
> >>>
> >>> // With 'as' cast
> >>>    29238.117    1880   15.552
> >>> System.Xml.XmlNode::SelectSingleNode(string,XmlNamespaceManager)
> >>>     Callers (with count) that contribute at least for 1%:
> >>>           1880  100 % System.Xml.XmlNode::SelectSingleNode(string)
> >>>
> >>>
> >>> I read that this is because 'as' cast generates IL instr 'isinst' while
> >>> 'cstyle' cast generates 'castclass'.
> >>>
> >>> The msdn documentation about XmlNode.SelectSingleNode doesn't state that
> >>> an InvalidCastException, can/could be thrown.
> >>>
> >>> Is this a sensible thing to do? If so could someone review/commit my
> >>> patch as I believe it will make a fairly major difference for
> >>> applications that make much use of SelectSingleNode.
> >>>
> >>>
> >>> Thanks
> >>> Tom
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> Mono-devel-list mailing list
> >>> Mono-devel-list at lists.ximian.com
> >>> http://lists.ximian.com/mailman/listinfo/mono-devel-list
> >>>
> >>>
> >> _______________________________________________
> >> Mono-devel-list mailing list
> >> Mono-devel-list at lists.ximian.com
> >> http://lists.ximian.com/mailman/listinfo/mono-devel-list
> >>
> >>
> >>
> >>
> >
> > _______________________________________________
> > Mono-devel-list mailing list
> > Mono-devel-list at lists.ximian.com
> > http://lists.ximian.com/mailman/listinfo/mono-devel-list
> >