Jan, That's going to be rather difficult given that the app has over 1000 files. Is there a way I can turn off the "default" options one at a time ? Thx -girish
--- Jan Hubicka <[EMAIL PROTECTED]> wrote: > > I have done quite a few experiments with this to > > narrow down the problem. The performance numbers > are > > slower compared to *No Feedback optimization with > just > > -O3* Here are some of them. All the experiments > were > > done on a new build-area in order to eliminate > effects > > of old feedback files. > > > > 1. I built the app using -O3 and > -fprofile-generate to > > generate the feedback data. I then ran the > workload > > and then recompiled the app using -O3 and > > -fprofile-use [app was 20% slower] > > > > 2. I built the app using -O3 and > -fprofile-generate to > > generate the feedback data. I then ran the > workload > > and then recompiled the app using -O3 and > > -fprofile-use -fno-vpt -fno-unroll-loops > > -fno-peel-loops -fno-tracer (Which is turn off all > the > > flags used by -fprofile-use) [App was still 20% > > slower] > > > > 3. I have tried selectively turning of some of the > > other flags in the above list as well, but the > > performance regression persists. > > > > 4. I tried with the older flags namely > -fprofile-arcs > > and -fbranch-probabilities still no help. > > So it looks like the slowdown is caused by one of > the profile based > optimizations that are enabled by default (basic > block reordering or > register allocation). If you are getting such a > noticable slodown, it > probably means that your app has pretty small inner > loop. Can you just > look into assembly generated for it with and without > profiling and try > to spot what is gong wrong? > > Thanks, > Honza > > > > Can someone help me out on how to proceed with > this. > > > > Thanks > > -girish > > > > > > --- Jan Hubicka <[EMAIL PROTECTED]> wrote: > > > > > > I started with a clean slate in my build > > > environment > > > > and did not have any residual files hanging > > > around. > > > > Are the steps I have indicated in my earlier > email > > > > correct. Is there a way I can break down the > > > problem > > > > into a smaller sub-set of flags and eliminate > the > > > flag > > > > causing the performance problem. What I mean > is > > > since > > > > -fprofile-generate and -fprofile-use enable a > > > bunch of > > > > flags, would it make sense to avoid profiling > and > > > try > > > > out some of the individual flags on a trial > and > > > error > > > > basis. If so what would be the flags to start > the > > > It would be probably better to just turn off the > > > individual > > > optimizations with -fprofile-use (for > optimizations > > > that are implied by > > > this flag there should be no need to re-profile > each > > > time). > > > If you can find particular optimization that > gets > > > out of control, it > > > would be lot easier to fix it... > > > > > > Honza > > > > trials with. > > > > > > > > -girish > > > > > > > > --- Jan Hubicka <[EMAIL PROTECTED]> wrote: > > > > > > > > > > On Wed, Jul 20, 2005 at 10:45:01AM -0700, > > > girish > > > > > vaitheeswaran wrote: > > > > > > > > --- Steven Bosscher <[EMAIL PROTECTED]> > > > wrote: > > > > > > > > > > > > > > > > > On Wednesday 20 July 2005 18:53, > girish > > > > > vaitheeswaran wrote: > > > > > > > > > > I am seeing a 20% slowdown with > > > feedback > > > > > optimization. > > > > > > > > > > Does anyone have any thoughts on > this. > > > > > > > > > > > > > > > > > > My first thought is that you should > > > probably > > > > > first > > > > > > > > > tell what compiler > > > > > > > > > you are using. > > > > > > > > > > > > > > I am using gcc 3.4.3 > > > > > > > -girish > > > > > > > > > > > > Which platform? I've seen slower code for > > > > > profile-directed optimizations > > > > > > on powerpc64-linux with GCC 4.0 and > mainline. > > > > > It's a bug, but I haven't > > > > > > looked into it enough to provide a small > test > > > case > > > > > for a problem report. > > > > > > > > > > Actually I would be very interested in > seeing > > > > > testcases such as those. > > > > > (and the Girish' slowdown too if possible). > In > > > > > general some slowdowns > > > > > in side corners are probably unavoidable but > > > both > > > > > 3.4.3 and 4.0 seems to > > > > > have pretty consistent improvements with > > > profiling > > > > > at least for SPEC and > > > > > i386 I am testing pretty regularly. > > > > > Such slodowns usually indicate problems like > > > > > incorrectly updated profile > > > > > or incorrectly readed in profile because of > > > > > missmatch in CFGs in between > > > > > profile and feedback run that are rather > > > dificult to > > > > > notice and hunt > > > > > down... > > > > > > > > > > Honza > > > > > > > > > > > > Janis > > > > > > > > >
