Re: [PATCH 1/3] perf tools: Cache register accesses for unwind processing

[Namhyung Kim <namhyung@kernel.org>]

Hi Jiri,

2014-04-28 (월), 11:48 +0200, Jiri Olsa:
> On Sun, Apr 27, 2014 at 11:29:21PM +0900, Namhyung Kim wrote:
> > Hi Jiri,
> > 
> > 2014-04-17 (목), 19:39 +0200, Jiri Olsa:
> > > Caching registers value into an array. Got about 4% speed up
> > > of perf_reg_value function for report command processing
> > > dwarf unwind stacks.
> > 
> > I'm not familiar with the code base, so probably silly questions:  Where
> > does the speed up come from?  IOW I don't know what's the difference
> > between the regs->regs and regs->cached_regs.  And does the cached_regs
> > contain correct values of registers for each frame?
> 
> the current way register's value is accessed is to get its
> index in the sample's regs array.. based on register's id
> and the registers mask
> 
> so each time you want register value you traverse the registers
> mask and count reg's index for the sample regs array
> 
> this patch does this only once for each register (at the time it's
> first accessed) and cache its value in the array (cache_regs). The
> cache_mask is used to identify which regs are already cached.

That means it'll get the same value everytime it accesses a register in
frames in a sample?

Thanks,
Namhyung