From romain.francois at dbmail.com  Tue Mar  3 18:27:35 2009
From: romain.francois at dbmail.com (Romain Francois)
Date: Tue, 03 Mar 2009 18:27:35 +0100
Subject: [Rd] profiler and loops
In-Reply-To: <49AD5988.4060104@dbmail.com>
References: <49AD238A.1060502@dbmail.com> <49AD5988.4060104@dbmail.com>
Message-ID: <49AD6887.4030206@dbmail.com>

Please ignore the previous patch which did not take into account the 
conditional compilation of doprof on windows. This one does, but was not 
tested on windows.

Romain

Romain Francois wrote:
>
> Hello,
>
> Please find attached a patch against svn implementing this proposal.
>
> The part I don't fully understand is the part involving the function  
> loopWithContect, so I've put "[loop]" in there instead of "[for]", 
> "[while]" or "[repeat]" because I don't really know how to extract the 
> information.
>
> With the script1 from my previous post, summaryRprof produces this:
>
> []$ /home/romain/workspace/R-trunk/bin/Rscript script1.R
> $by.self
>        self.time self.pct total.time total.pct
> "[for]"      5.32     98.9       5.38     100.0
> "rnorm"      0.06      1.1       0.06       1.1
>
> $by.total
>        total.time total.pct self.time self.pct
> "[for]"       5.38     100.0      5.32     98.9
> "rnorm"       0.06       1.1      0.06      1.1
>
> $sampling.time
> [1] 5.38
>
> Romain
>
>
> Romain Francois wrote:
>> Hello,
>>
>> (This is follow up from this thread: 
>> http://www.nabble.com/execution-time-of-.packages-td22304833.html but 
>> with a different focus)
>>
>> I am often confused by the result of the profiler, when a loop is 
>> involved. Consider these two scripts:
>>
>> script1:
>>
>> Rprof( )
>> x <- numeric( )
>>   for( i in 1:10000){
>>     x <- c( x, rnorm(10) )
>>   }
>> Rprof( NULL )
>> print( summaryRprof( ) )
>>
>>
>> script2:
>>
>> Rprof( )
>> ffor <- function(){
>>   x <- numeric( )
>>   for( i in 1:10000){
>>     x <- c( x, rnorm(10) )
>>   }
>> }
>> ffor()
>> Rprof( NULL )
>> print( summaryRprof( ) )
>>
>>
>> []$ time Rscript --vanilla script1.R
>> $by.self
>>       self.time self.pct total.time total.pct
>> "rnorm"      0.22      100       0.22       100
>>
>> $by.total
>>       total.time total.pct self.time self.pct
>> "rnorm"       0.22       100      0.22      100
>>
>> $sampling.time
>> [1] 0.22
>>
>> real    0m7.786s
>> user    0m5.192s
>> sys     0m0.735s
>>
>> []$$ time Rscript --vanilla script2.R
>> $by.self
>>       self.time self.pct total.time total.pct
>> "ffor"       4.94     92.5       5.34     100.0
>> "rnorm"      0.40      7.5       0.40       7.5
>>
>> $by.total
>>       total.time total.pct self.time self.pct
>> "ffor"        5.34     100.0      4.94     92.5
>> "rnorm"       0.40       7.5      0.40      7.5
>>
>> $sampling.time
>> [1] 5.34
>>
>>
>> real    0m7.841s
>> user    0m5.152s
>> sys     0m0.712s
>>
>>
>>
>> In the first one, I call a for loop from the top level and in the 
>> second one, the loop is wrapped in a function call. This shows the 
>> inability of the profiler to point loops as responsible for 
>> bottlenecks. The coder of script1 would not know what to do to 
>> improve on the script.
>>
>> I have had a quick look in the code, and here are a few thoughts:
>>
>> in the function "doprof" in eval.c,  this loop write the call stack 
>> on the profiler file:
>>
>> for (cptr = R_GlobalContext; cptr; cptr = cptr->nextcontext) {
>>   if ((cptr->callflag & (CTXT_FUNCTION | CTXT_BUILTIN))
>>       && TYPEOF(cptr->call) == LANGSXP) {
>>       SEXP fun = CAR(cptr->call);
>>       if (!newline) newline = 1;
>>       fprintf(R_ProfileOutfile, "\"%s\" ",
>>           TYPEOF(fun) == SYMSXP ? CHAR(PRINTNAME(fun)) :
>>           "<Anonymous>");
>>   }
>>   }
>>  so we can see it only cares about context CTXT_FUNCTION and 
>> CTXT_BUILTIN, when for loops play with CTXT_LOOP (this is again in 
>> eval.c within the do_for function)
>>
>> begincontext(&cntxt, CTXT_LOOP, R_NilValue, rho, R_BaseEnv, R_NilValue,
>>        R_NilValue);
>>
>> which as the name implies, begins the context of the for loop. The 
>> begincontext function looks like this :
>>
>> void begincontext(RCNTXT * cptr, int flags,
>>         SEXP syscall, SEXP env, SEXP sysp,
>>         SEXP promargs, SEXP callfun)
>> {
>>   cptr->nextcontext = R_GlobalContext;
>>   cptr->cstacktop = R_PPStackTop;
>>   cptr->evaldepth = R_EvalDepth;
>>   cptr->callflag = flags;
>>   cptr->call = syscall;
>>   cptr->cloenv = env;
>>   cptr->sysparent = sysp;
>>   cptr->conexit = R_NilValue;
>>   cptr->cend = NULL;
>>   cptr->promargs = promargs;
>>   cptr->callfun = callfun;
>>   cptr->vmax = vmaxget();
>>   cptr->intsusp = R_interrupts_suspended;
>>   cptr->handlerstack = R_HandlerStack;
>>   cptr->restartstack = R_RestartStack;
>>   cptr->prstack = R_PendingPromises;
>> #ifdef BYTECODE
>>   cptr->nodestack = R_BCNodeStackTop;
>> # ifdef BC_INT_STACK
>>   cptr->intstack = R_BCIntStackTop;
>> # endif
>> #endif
>>   R_GlobalContext = cptr;
>> }
>>
>>
>> So it could be possible to set the last argument of the begincontext 
>> function to "for" and use this code in the doprof function:
>>
>>
>> for (cptr = R_GlobalContext; cptr; cptr = cptr->nextcontext) {
>> if ( ( cptr->callflag & (CTXT_FUNCTION | CTXT_BUILTIN ) )
>>       && TYPEOF(cptr->call) == LANGSXP) {
>>       SEXP fun = CAR(cptr->call);
>>       if (!newline) newline = 1;
>>       fprintf(R_ProfileOutfile, "\"%s\" ",
>>           TYPEOF(fun) == SYMSXP ? CHAR(PRINTNAME(fun)) :
>>           "<Anonymous>");
>>   } else if( cptr->callflag & CTXT_LOOP){
>>     SEXP fun = CAR(cptr->syscall);
>>     if (!newline) newline = 1;
>>     fprintf(R_ProfileOutfile, "\"%s\" ", CHAR(PRINTNAME(fun)) );
>>   }
>> }
>>
>> so that we see for in the list of "functions" that appear in the 
>> profiler file.
>>
>> Obviously I am taking some shortcuts here, because of the other 
>> loops, but I would like to make a formal patch with this. Before I do 
>> that, I'd like to know :
>> - is this has a chance of breaking something else (does the CTXT_LOOP 
>> being R_NilValue is used elsewhere)
>> - would this feature be welcome.
>> - Should I differentiate real functions with loops in the output 
>> file, maybe I can write "[for]" instead of for to emphacize this is 
>> not a function.
>>
>> Romain
>>

-- 
Romain Francois
Independent R Consultant
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr


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[Rd] profiler and loops
Romain Francois