linux-kernel - Drop WARN on AMD lack of perfctrs

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Message-ID: <20130516151026.GB18325@hansolo.jdub.homelinux.org>
Date:	Thu, 16 May 2013 11:10:26 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, gleb@...hat.com
Subject: Drop WARN on AMD lack of perfctrs

Hi All,

If you boot a KVM guest on an AMD family 15h and specify -cpu host,
you'll get the following splat:

[    0.031000] ------------[ cut here ]------------
[    0.031000] WARNING: at arch/x86/kernel/cpu/perf_event_amd.c:772
amd_pmu_init+0x18c/0x249()
[    0.031000] Hardware name: Bochs
[    0.031000] Odd, counter constraints enabled but no core perfctrs
detected!
[    0.031000] Modules linked in:

[    0.031000] Pid: 1, comm: swapper/0 Not tainted
3.9.0-0.rc1.git0.4.fc19.x86_64 #1
[    0.031000] Call Trace:
[    0.031000]  [<ffffffff81d10c67>] ? amd_pmu_init+0x18c/0x249
[    0.031000]  [<ffffffff8105c9a0>] warn_slowpath_common+0x70/0xa0
[    0.031000]  [<ffffffff81d106b3>] ? check_bugs+0x2d/0x2d
[    0.031000]  [<ffffffff8105ca1c>] warn_slowpath_fmt+0x4c/0x50
[    0.031000]  [<ffffffff81d10c67>] amd_pmu_init+0x18c/0x249
[    0.031000]  [<ffffffff81d106e7>] init_hw_perf_events+0x34/0x428
[    0.031000]  [<ffffffff81d106b3>] ? check_bugs+0x2d/0x2d
[    0.031000]  [<ffffffff8100210a>] do_one_initcall+0x10a/0x160
[    0.031000]  [<ffffffff81d06fa5>] kernel_init_freeable+0xcf/0x1fa
[    0.031000]  [<ffffffff81629800>] ? rest_init+0x80/0x80
[    0.031000]  [<ffffffff8162980e>] kernel_init+0xe/0x190
[    0.031000]  [<ffffffff8164e22c>] ret_from_fork+0x7c/0xb0
[    0.031000]  [<ffffffff81629800>] ? rest_init+0x80/0x80
[    0.031000] ---[ end trace a1e57d3cb8668105 ]---

That seems a bit excessive, and it gets picked up by auto-reporting
tools like ABRT as a bug.  Can we remove the WARN and just use pr_err or
something else instead?

josh
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