Differences in malloc between 6 and 7?

[Brooks Davis]

[added jasone@ to the cc list]

On Mon, Mar 03, 2008 at 03:23:33PM -0500, gnn at freebsd.org wrote:
> Hi,
> 
> One of the folks I'm working with found this.  The following code,
> which yes, is just an example, is 1/2 as fast on 7.0-RELEASE as on
> 6.3.  Where should I look to find out why?

All of malloc lives in src/libc/stdlib/malloc.c.  I know Jason has made
some changes in current so it might be worthwhile grabbing a copy from
there and seeing if this case works better there.

-- Brooks

> 
> Best,
> George
> 

> 
> culprit continues to be arena_run_malloc, which takes several times longer
> on fbsd7 than the total of all calls to *alloc* on fbsd6.
> 
> Output of uname -a:
> FreeBSD testlab5 7.0-STABLE FreeBSD 7.0-STABLE #1: Thu Feb 28 10:06:47 EST
> 2008     root at builder:/usr/obj/usr/sources/FreeBSD.7/src/sys/GENERIC  amd64
> 
> Program source:
> // simple test program that shows fbsd7 memory operations 2x slower than
> fbsd6
> // compile with:
> //  g++ -o memory.o -c -O3 -Wall memory.cc
> //  g++ -o memory memory.o -O3 -L/usr/local/lib
> 
> 
> class MemUser {
>   public:
>     void nTimesInOrder(int n) { for (int i=0; i<n; ++i) { alloc();
> freeInOrder(); } }
>     void alloc();
>     void freeInOrder();
>     void freeRandom();
> 
>   private:
>     char* p;
>     char* ptrs[16384];
>     int psize;
> };
> 
> void MemUser::alloc()
> {
>     int n = 0;
>     // for now, allocating 1000 times at each size.  Sizes are 2, 20, 200,
> 2000, 20k, 200k bytes
>     for (int size=2; size <= 2e5; size *= 10) {
>         for (int i=0; i<1000; ++i) {
>             p = new char [size];
>             ptrs[n++] = p;
>         }
>     }
>     psize = n;
> }
> 
> void MemUser::freeInOrder()
> {
>     for (int i=0; i < psize; ++i) {
>         delete [] ptrs[i];
>     }
> }
> 
> 
> int main(int argc, char* argv[])
> {
>     MemUser mu;
>     mu.nTimesInOrder(5000);
> }
> 
> 

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