Messages in this thread | | | Date | Wed, 6 May 2009 09:47:34 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 10/11] ring-buffer: move big if statement down |
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On Wed, 6 May 2009, Ingo Molnar wrote:
> > * Steven Rostedt <rostedt@goodmis.org> wrote: > > > This patch changes it to a goto: > > > > code; > > > > if (cross to next page) > > goto next_page; > > > > more code; > > > > return; > > > > next_page: > > > > [ lots of code] > > I have pulled it, but could you please change it to a helper > function instead? There's almost never a good reason to combine > 'more code' with 'lots of code' in a single function. It also > documents the unlikeliness, etc.
As I stated in the change log, I did not want to convert it to a helper function because it uses the variables created before. It would end up going from:
if (write > BUF_PAGE_SIZE) goto next_page;
to:
if (write > BUF_PAGE_SIZE) return rb_move_tail(cpu_buffer, length, tail, commit_page, tail_page);
Although it is the "unlikely" case, it is still a fast path. It happens every time a write into the page buffer crosses a page boundary. Since it is only used once, gcc would hopefully inline it. If it does not, then we are copying a bunch of parameters for nothing.
I could still do this and see what gcc does with it.
-- Steve
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