From: Ingo Molnar <mingo@kernel.org>
To: "Ghannam, Yazen" <Yazen.Ghannam@amd.com>
Cc: Borislav Petkov <bp@alien8.de>, x86-ml <x86@kernel.org>,
Yves Dionne <yves.dionne@gmail.com>,
Brice Goglin <Brice.Goglin@inria.fr>,
Peter Zijlstra <peterz@infradead.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] x86/CPU/AMD: Bring back Compute Unit ID
Date: Thu, 2 Feb 2017 17:29:01 +0100 [thread overview]
Message-ID: <20170202162901.GB12498@gmail.com> (raw)
In-Reply-To: <CY4PR12MB164014100E42E4970B846B18F84C0@CY4PR12MB1640.namprd12.prod.outlook.com>
* Ghannam, Yazen <Yazen.Ghannam@amd.com> wrote:
> Here are my results on a 32C Bulldozer system with an SSD. Also, I use ccache so
> I added "ccache -C" in the pre-build script so the cache gets cleared.
>
> Before:
> Performance counter stats for 'make -s -j65 bzImage' (3 runs):
>
> 2375752.777479 task-clock (msec) # 23.589 CPUs utilized ( +- 0.35% )
> 1,198,979 context-switches # 0.505 K/sec ( +- 0.34% )
> 8,964,671,259 cache-misses ( +- 0.44% )
> 79,399 cpu-migrations # 0.033 K/sec ( +- 1.92% )
> 37,840,875 page-faults # 0.016 M/sec ( +- 0.20% )
> 5,425,612,846,538 cycles # 2.284 GHz ( +- 0.36% )
> 3,367,750,745,825 instructions # 0.62 insn per cycle ( +- 0.11% )
> 750,591,286,261 branches # 315.938 M/sec ( +- 0.11% )
> 43,544,059,077 branch-misses # 5.80% of all branches ( +- 0.08% )
>
> 100.716043494 seconds time elapsed ( +- 1.97% )
>
> After:
> Performance counter stats for 'make -s -j65 bzImage' (3 runs):
>
> 1736720.488346 task-clock (msec) # 23.529 CPUs utilized ( +- 0.16% )
> 1,144,737 context-switches # 0.659 K/sec ( +- 0.20% )
> 8,570,352,975 cache-misses ( +- 0.33% )
> 91,817 cpu-migrations # 0.053 K/sec ( +- 1.67% )
> 37,688,118 page-faults # 0.022 M/sec ( +- 0.03% )
> 5,547,082,899,245 cycles # 3.194 GHz ( +- 0.19% )
> 3,363,365,420,405 instructions # 0.61 insn per cycle ( +- 0.00% )
> 749,676,420,820 branches # 431.662 M/sec ( +- 0.00% )
> 43,243,046,270 branch-misses # 5.77% of all branches ( +- 0.01% )
>
> 73.810517234 seconds time elapsed ( +- 0.02% )
That's pretty impressive: ~35% difference in wall clock performance of this
workload.
And that while both the cycles and the instructions count is within 2.5% of each
other. The only stat the differs beyond the level of noise is cache-misses:
8,964,671,259 cache-misses ( +- 0.44% )
8,570,352,975 cache-misses ( +- 0.33% )
which is 4.5%, but I have trouble believing that just 4.5% more cachemisses can
have such a massive effect on performance.
So unless +4.5% cachemisses can cause a 35% difference in performance this is a
really weird result. Where did the extra performance come from - was the 'good'
workload perhaps running at higher CPU frequencies for some reason?
Thanks,
Ingo
prev parent reply other threads:[~2017-02-02 16:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-01 20:02 [RFC PATCH] x86/CPU/AMD: Bring back Compute Unit ID Borislav Petkov
2017-02-01 21:37 ` Ghannam, Yazen
2017-02-01 21:44 ` Borislav Petkov
2017-02-01 21:55 ` Ghannam, Yazen
2017-02-01 22:25 ` Borislav Petkov
2017-02-01 22:41 ` Borislav Petkov
2017-02-02 12:10 ` Borislav Petkov
2017-02-02 15:43 ` Borislav Petkov
2017-02-02 16:09 ` Ingo Molnar
2017-02-02 17:04 ` Borislav Petkov
2017-02-02 18:10 ` Borislav Petkov
2017-02-02 20:45 ` Ghannam, Yazen
2017-02-02 16:14 ` Ghannam, Yazen
2017-02-02 16:29 ` Ingo Molnar [this message]
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