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* Re: [Lse-tech] gcc 2.95 vs 3.21 performance
@ 2003-02-10 20:13 Albert Cahalan
  2003-02-10 20:49 ` Falk Hueffner
  0 siblings, 1 reply; 6+ messages in thread
From: Albert Cahalan @ 2003-02-10 20:13 UTC (permalink / raw)
  To: linux-kernel; +Cc: velco, mbligh, davej, ak

Momchil Velikov writes:
> "Martin" == Martin J Bligh <mbligh@aracnet.com> writes:

>> But the point is still the same ... even if it is doing
>> more agressive optimisation, it's not actually buying us
>> anything (at least for the kernel)
>
> which might be due in part to ``-fno-strict-aliasing''
> used to compile the Linux kernel.

This is fixable for any gcc implementing __may_alias__.

Linux uses -fno-strict-aliasing because people like
to cast a (foo*) to an (int*) instead of using a
union or (char*) as required by the C language.
When -fno-strict-aliasing was added to the command
line, gcc did not offer the __may_alias__ attribute.

BTW, in case any gcc hacker is paying attention,
the documentation fails to mention the gcc version
required for this or any other attribute. Also it
would be nice to have an option to ditch the (char*)
exception; it's junk when you have __may_alias__.



^ permalink raw reply	[flat|nested] 6+ messages in thread
* gcc 2.95 vs 3.21 performance
@ 2003-02-03 23:05 Martin J. Bligh
  2003-02-03 23:22 ` [Lse-tech] " Andi Kleen
  2003-02-04 12:20 ` Dave Jones
  0 siblings, 2 replies; 6+ messages in thread
From: Martin J. Bligh @ 2003-02-03 23:05 UTC (permalink / raw)
  To: linux-kernel; +Cc: lse-tech

People keep extolling the virtues of gcc 3.2 to me, which I'm
reluctant to switch to, since it compiles so much slower. But
it supposedly generates better code, so I thought I'd compile
the kernel with both and compare the results. This is gcc 2.95
and 3.2.1 from debian unstable on a 16-way NUMA-Q. The kernbench
tests still use 2.95 for the compile-time stuff.

The results below leaves me distinctly unconvinced by the supposed 
merits of modern gcc's. Not really better or worse, within experimental
error. But much slower to compile things with.

Kernbench-2: (make -j N vmlinux, where N = 2 x num_cpus)
                                   Elapsed        User      System         CPU
                        2.5.59       46.08      563.88      118.38     1480.00
                 2.5.59-gcc3.2       45.86      563.63      119.58     1489.33

Kernbench-16: (make -j N vmlinux, where N = 16 x num_cpus)
                                   Elapsed        User      System         CPU
                        2.5.59       47.45      568.02      143.17     1498.17
                 2.5.59-gcc3.2       47.15      567.41      143.72     1507.50

DISCLAIMER: SPEC(tm) and the benchmark name SDET(tm) are registered
trademarks of the Standard Performance Evaluation Corporation. This 
benchmarking was performed for research purposes only, and the run results
are non-compliant and not-comparable with any published results.

Results are shown as percentages of the first set displayed

SDET 1  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         0.8%
                 2.5.59-gcc3.2        95.3%         5.2%

SDET 2  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         0.6%
                 2.5.59-gcc3.2        91.9%         7.1%

SDET 4  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         5.7%
                 2.5.59-gcc3.2        98.8%         5.3%

SDET 8  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         1.4%
                 2.5.59-gcc3.2       105.3%         4.7%

SDET 16  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         1.7%
                 2.5.59-gcc3.2       103.1%         1.8%

SDET 32  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         1.5%
                 2.5.59-gcc3.2       101.0%         1.6%

SDET 64  (see disclaimer)
                                Throughput    Std. Dev
                        2.5.59       100.0%         0.7%
                 2.5.59-gcc3.2       103.1%         1.1%

SDET 128  (see disclaimer)
                                Throughput    Std. Dev

NUMA schedbench 4:
                                   AvgUser     Elapsed   TotalUser    TotalSys
                        2.5.59        0.00       38.88       82.78        0.65
                 2.5.59-gcc3.2        0.00       41.80      107.76        0.73

NUMA schedbench 8:
                                   AvgUser     Elapsed   TotalUser    TotalSys
                        2.5.59        0.00       49.30      247.80        1.93
                 2.5.59-gcc3.2        0.00       38.00      229.83        2.11

NUMA schedbench 16:
                                   AvgUser     Elapsed   TotalUser    TotalSys
                        2.5.59        0.00       57.37      843.12        3.77
                 2.5.59-gcc3.2        0.00       57.28      839.21        2.85

NUMA schedbench 32:
                                   AvgUser     Elapsed   TotalUser    TotalSys
                        2.5.59        0.00      116.99     1805.79        6.05
                 2.5.59-gcc3.2        0.00      118.44     1788.09        6.25

NUMA schedbench 64:
                                   AvgUser     Elapsed   TotalUser    TotalSys
                        2.5.59        0.00      235.18     3632.73       15.45
                 2.5.59-gcc3.2        0.00      234.55     3633.76       15.02



------------------------------------------------------------------------------


And with the same kernel, comparing the compile times for gcc 2.95 to 3.2

Kernbench-2: (make -j N vmlinux, where N = 2 x num_cpus)
                                   Elapsed        User      System         CPU
                        gcc2.95      46.08      563.88      118.38     1480.00
                        gcc3.21      69.93      923.17      114.36     1483.17

Kernbench-16: (make -j N vmlinux, where N = 16 x num_cpus)
                                   Elapsed        User      System         CPU
                        gcc2.95      47.45      568.02      143.17     1498.17
                        gcc3.21      71.44      926.45      134.89     1485.33

pft.


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2003-02-10 20:39 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2003-02-10 20:13 [Lse-tech] gcc 2.95 vs 3.21 performance Albert Cahalan
2003-02-10 20:49 ` Falk Hueffner
  -- strict thread matches above, loose matches on Subject: below --
2003-02-03 23:05 Martin J. Bligh
2003-02-03 23:22 ` [Lse-tech] " Andi Kleen
2003-02-04 12:20 ` Dave Jones
2003-02-04 15:50   ` Martin J. Bligh
2003-02-10 12:13     ` Momchil Velikov

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