Re: [patch 2/9] Conditional Calls - Hash Table

Mathieu Desnoyers
2007-06-01T18:04:13Z

* Matt Mackall (mpm@selenic.com) wrote:
> On Fri, Jun 01, 2007 at 12:46:23PM -0400, Mathieu Desnoyers wrote:
> > * Matt Mackall (mpm@selenic.com) wrote:
> > > On Thu, May 31, 2007 at 03:42:50PM +0200, Andi Kleen wrote:
> > > > Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> writes:
> > > >
> > > > > Reimplementation of the cond calls which uses a hash table to hold the active
> > > > > cond_calls. It permits to first arm a cond_call and then load supplementary
> > > > > modules that contain this cond_call.
> > > >
> > > > Hash table is probably overkill. This is a very very slow path operation.
> > > > Can you simplify the code? Just a linked list of all the condcall segments
> > > > should be enough and then walk it.
> > >
> > > I think it could be greatly simplified by using symbols instead of
> > > strings.
> > >
> > > That is, doing cond_call(foo, func()) rather than cond_call("foo",
> > > func()). Here foo is a structure or type holding the relevant info to
> > > deal with the cond_call infrastructure. For unoptimized architectures,
> > > it can simply be a bool, which will be faster.
> > >
> > > This has the added advantage that the compiler will automatically pick
> > > up any misspellings of these things. And it saves the space we'd use
> > > on the hash table too.
> > >
> >
> > The idea is interesting, but does not fit the problem: AFAIK, it will
> > not be possible to do multiple declarations of the same symbol, which is
> > needed whenever we want to declare a cond_call() more than once or to
> > embed it in an inline function.
>
> It's not clear to me why either of those things are necessary. An
> example please?
>

Case where we want to declare the same cond_call multiple times :

function_a(int var)
{
...
cond_call(profile_on, profile_hit(...));
...
}

function_b(int var, int var2)
{
...
cond_call(profile_on, profile_hit(...));
...
}

Case in inline function :

static inline myinlinefct()
{
...
cond_call(profile_on, profile_hit(...));
...
}

somefct()
{
...
myinlinefct();
...
myinlinefct();
...
}

Those will result in multiple declarations of the cond_call.