(bouncing to linaro-dev as it's generally interesting) On Fri, Sep 16, 2011 at 8:17 AM, Ramana Radhakrishnan <ramana.radhakrish...@linaro.org> wrote: > Hi, > > I've been looking at some of the perf regressions we've been seeing > these days in an attempt to understand what's going on in these cases. > While I can use perf and get more statistics and do other things to > figure out why there are perf regressions between 2 binaries along > with perf record and report, I wonder if it is possible to use u-boot > to accurately measure what's going on. I would like to try and get the > values of the performance counters between 2 program points . > > I am aware that there are patches that are floating around that allow > users to set and reset the PMU counters by allowing user level access > to it in the kernel : while that maybe useful to some I'm not sure if > I want to take a chance with some other process getting scheduled that > ends up getting scheduled. Even if there are parts of the kernel that > save and restore PMU counters associated per process with across > context switches . I'm looking for as accurate measurements as > possible in this case and I wonder if u-boot is the best bet for this > ( in the absence of any dedicated hardware debug / trace unit) given > not all of us have one. > > > At the minimum to do this I believe we require u-boot or some start-up code > to: > > * Turn on i-cache and d-cache. ( The current u-boot for panda that I > get from the linaro-uboot git repo > git://git.linaro.org/boot/u-boot-linaro-stable.git says "Warning > Caches turned off" when starting up ). Googling around I find a few > patches floating around that turn on the d-cache in August from Aneesh > at TI . We should consider getting these in at some point. > > * Looking in $(UBOOT_TOP)/examples/api I see that there are simple > printf routines and simple stand-alone applications that exist which > could be used for this purpose. The one problem with this is the fact > that u-boot appears to require use of -ffixed-r8 for it's purposes > which *might* mean we need these if we were to use API calls into > standard u-boot functions .
I wonder if R8 is used in the current ARM version? There's no reason we can't cherry pick parts such as the serial I/O out into a library and make the app completely self contained. Skip all of the initialisation stuff and assume the boot loader has done it for you. > * Turn on / off speculative prefetching - I believe the kernel does > this already for a few boards, but could this be done in u-boot just > before it launches a test application ? > > * Turn on the VFP and Neon units. > > * Turn on unaligned access so that unaligned accesses are allowed in > the test applications. GCC will now move towards generating unaligned > accesses on versions of the architecture that support it, the patches > upstream have now been approved. > > * Memory map / linker scripts to make sure we are putting things in > the right places (sigh, has to be per-board). But everything goes in RAM so you have one generic linker script and a per board MEMORY definition. Similar to: http://bazaar.launchpad.net/~stm32f-dev/stm32f-dev/stm32f-startup/view/head:/src/stm32f103xb.ld ...but even lighter. > We then write a set of library functions that could then look at what > performance counters are of interest to us and track them by resetting > them to 0 and making sure they haven't overflown. > > Has anyone else in the group played with u-boot before or has any > thoughts in this direction ? I am not suggesting that we do this work > right now but it sounds like an interesting thought of where we can > get to with this. My worry is that we miss turning on a feature and get results that aren't representative. That should be easy enough to check by baselineing against a Linux hosted run. We can use NFS or kermit to load the programs. u-boot has a network console which is nice when you don't have serial. This combined with an expect script (or LAVA? Paul?) should automate the whole process. -- Michael _______________________________________________ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-toolchain
