Re: [PATCH v7 19/36] function_graph: Implement fgraph_reserve_data() and fgraph_retrieve_data()

[Google]

On Wed, 14 Feb 2024 18:54:07 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Thu, 15 Feb 2024 08:45:52 +0900
> Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote:
> 
> > > Hmm, the above is a fast path. I wonder if we should add a patch to make that into:
> > > 
> > > 	if (unlikely(size_bytes & (sizeof(long) - 1)))
> > > 		data_size = DIV_ROUND_UP(size_bytes, sizeof(long));
> > > 	else
> > > 		data_size = size_bytes >> (sizeof(long) == 4 ? 2 : 3);
> > > 
> > > to keep from doing the division.  
> > 
> > OK, I thought DIV_ROUND_UP was not much cost. Since sizeof(long) is
> > fixed 4 or 8, so 
> > 
> > data_size = (size_bytes + sizeof(long) - 1) >> BITS_PER_LONG;
> > 
> > will this work?
> 
> No, because BITS_PER_LONG is 32 or 64 ;-)

Oops indeed.

> 
> But this should;
> 
> 	data_size = (size_bytes + sizeof(long) - 1) >> (sizeof(long) == 4 ? 2 : 3);
> 
> As sizeof(long) is a constant, that conditional expression will be hard
> coded into either 2 or 3 by the compiler.

Yeah. OK, let me update it.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>