linux-kernel - Re: [PATCH 1/1] x86_64: add config options to optimize for newer AMD processors

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Message-ID: <20131003165740.GA17417@pd.tnic>
Date:	Thu, 3 Oct 2013 18:57:40 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Linux-Kernel mailing list <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...hat.com>
Subject: Re: [PATCH 1/1] x86_64: add config options to optimize for newer AMD
 processors

On Thu, Oct 03, 2013 at 09:27:45AM -0700, Linus Torvalds wrote:
> On Thu, Oct 3, 2013 at 5:06 AM, Austin S Hemmelgarn
> <ahferroin7@...il.com> wrote:
> > improved.  Building kernel 3.12-rc2 with allmodconfig using 8 jobs on a FX-8320 takes
> >
> > 22 minutes and 57 seconds on a kernel with CONFIG_MK8,
> > 21 minutes and 35 seconds on a kernel with CONFIG_GENERIC, and
> > 19 minutes and 11 seconds on a kernel with CONFIG_PILEDRIVER.
> 
> That's certainly noticeable. Surprisingly so. What makes MK8 so bad in
> particular, I wonder?
> 
> Just out of interest, have you done any profiles on the kernel cost
> here to see what it is that makes such a big difference. Because
> normally on a kernel build, I see most of the overhead in path lookup.
> But that's only true for otherwise optimized builds that don't have
> system call auditing etc debugging that spreads the costs out over
> everything..

Yeah, I was having some doubts about the numbers above so I ran my own
benchmarking, machine is a Piledriver box:

vendor_id       : AuthenticAMD
cpu family      : 21
model           : 2
model name      : AMD FX(tm)-8350 Eight-Core Processor
stepping        : 0

and I don't really see any of those improvements above. Actually,
-march=bdver2 is even slightly worse in comparison to mk8.

And the workload is of building a config specific to that machine but
allmodconfig looks very similar, the numbers being simply higher.

$ zgrep MK8 /proc/config.gz
CONFIG_MK8=y

/home/boris/bin/perf stat --repeat 10 -a --sync --pre /home/boris/kernel/pre-build-kernel.sh make -s -j64 bzImage

 Performance counter stats for 'make -s -j64 bzImage' (10 runs):

    1081808.628840 task-clock                #    7.996 CPUs utilized            ( +-  0.06% ) [100.00%]
         1,203,753 context-switches          #    0.001 M/sec                    ( +-  0.04% ) [100.00%]
            48,748 cpu-migrations            #    0.045 K/sec                    ( +-  0.59% ) [100.00%]
        31,145,439 page-faults               #    0.029 M/sec                    ( +-  0.00% )
 3,836,736,801,500 cycles                    #    3.547 GHz                      ( +-  0.03% ) [100.00%]
   957,386,966,493 stalled-cycles-frontend   #   24.95% frontend cycles idle     ( +-  0.06% ) [100.00%]
   218,581,249,251 stalled-cycles-backend    #    5.70% backend  cycles idle     ( +-  0.06% ) [100.00%]
 2,466,632,641,972 instructions              #    0.64  insns per cycle
                                             #    0.39  stalled cycles per insn  ( +-  0.00% ) [100.00%]
   537,749,333,838 branches                  #  497.084 M/sec                    ( +-  0.00% ) [100.00%]
    27,802,940,176 branch-misses             #    5.17% of all branches          ( +-  0.00% )

     135.292843025 seconds time elapsed                                          ( +-  0.06% )


$ zgrep PILEDRIVER /proc/config.gz
CONFIG_MPILEDRIVER=y

/home/boris/bin/perf stat --repeat 10 -a --sync --pre /home/boris/kernel/pre-build-kernel.sh make -s -j64 bzImage

 Performance counter stats for 'make -s -j64 bzImage' (10 runs):

    1085723.230470 task-clock                #    7.996 CPUs utilized            ( +-  0.10% ) [100.00%]
         1,204,355 context-switches          #    0.001 M/sec                    ( +-  0.10% ) [100.00%]
            49,143 cpu-migrations            #    0.045 K/sec                    ( +-  0.76% ) [100.00%]
        31,196,575 page-faults               #    0.029 M/sec                    ( +-  0.00% )
 3,851,255,065,133 cycles                    #    3.547 GHz                      ( +-  0.02% ) [100.00%]
   958,840,197,117 stalled-cycles-frontend   #   24.90% frontend cycles idle     ( +-  0.09% ) [100.00%]
   220,260,399,411 stalled-cycles-backend    #    5.72% backend  cycles idle     ( +-  0.04% ) [100.00%]
 2,466,701,295,156 instructions              #    0.64  insns per cycle
                                             #    0.39  stalled cycles per insn  ( +-  0.00% ) [100.00%]
   537,992,040,195 branches                  #  495.515 M/sec                    ( +-  0.00% ) [100.00%]
    27,860,290,286 branch-misses             #    5.18% of all branches          ( +-  0.00% )

     135.784111961 seconds time elapsed                                          ( +-  0.10% )

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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