[PATCH v2][malloc] Use relaxed atomics for malloc have_fastchunks

[Wilco Dijkstra]

DJ Delorie wrote:
    
> Results of benchmarks...  Note that dj2 is a synthetic test, so the
> slowdown is not surprising, and that all tests are averages of 16 runs
> except git-cinnabar-helper which is only two pristine and one patched
> (it takes 20 minutes per run and I got impatient ;).  Values are cycles,
> lower is better.
>
> Workload                      Pristine         Patched      
> 389ds                     9,121,687,695    8,017,021,813   87.89%
> dj2                       7,901,004,232    8,277,784,940  104.77%
> git-cinnabar-helper     100,123,244,269  90,058,896,622   89.95%
> okular-1                  3,648,656,309    3,220,751,900   88.27%
> oocalc                    1,053,984,703    1,009,859,213   95.81%
> qemu-virtio                 781,260,028      766,458,246   98.11%
> qemu-win7                   655,497,193      626,270,566   95.54%
> proprietary-2             2,112,159,165    1,977,684,058   93.63%
>                        
>                                                Mean     94.25%
>
> Patch looks good to me otherwise, caveat any futher complaints about
> concurrency ;-)

Thanks, that looks very good indeed! Are these all multithreaded?
I'm working on a few tweaks to improve single-threaded performance.

Btw have you tried running these traces with say:
export GLIBC_TUNABLES=glibc.malloc.tcache_count=100

It would be interesting to find out whether that (or even larger values)
helps your traces too like it does the benchmarks I've tried.

Wilco