Re: [RFA] Use data cache for stack accesses

[Doug Evans <dje@google.com>]

On Wed, Aug 26, 2009 at 1:08 PM, Pedro Alves<pedro@codesourcery.com> wrote:
>> > Did you post number showing off the improvements from
>> > having the cache on?  E.g., when doing foo, with cache off,
>> > I get NNN memory reads, while with cache off, we get only
>> > nnn reads.  I'd be curious to have some backing behind
>> > "This improves remote performance significantly".
>>
>> For a typical gdb/gdbserver connection here a backtrace of 256 levels
>> went from 48 seconds (average over 6 tries) to 4 seconds (average over
>> 6 tries).
>
> Nice!  Were all those single runs started from cold cache, or
> are you starting from a cold cache and issuing 6 backtraces in
> a row?  I mean, how sparse were those 6 tries?  Shall one
> read that as 48,48,48,48,48,48 vs 20,1,1,1,1,1 (some improvement
> due to chunking, and large improvement due to caching in following
> repeats of the command); or 48,48,48,48,48,48 vs 4,4,4,4,4,4 (large
> improvement due to chunking --- caching not actually measured)?

The cache was always flushed between backtraces, so that's
48, 48. ..., 48 vs 4, 4, ..., 4.

Backtraces win from both chunking and caching.
Even in one backtrace gdb will often fetch the same value multiple times.
I haven't computed the relative win.