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From: Ingo Molnar <mingo@kernel.org>
To: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: WANG Chao <chao.wang@ucloud.cn>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Vikas Shivappa <vikas.shivappa@linux.intel.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Len Brown <len.brown@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Mathias Krause <minipli@googlemail.com>,
	x86@kernel.org, "Rafael J. Wysocki" <rafael@kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again
Date: Fri, 10 Nov 2017 08:25:13 +0100	[thread overview]
Message-ID: <20171110072513.mp5p7o7pledumoyi@gmail.com> (raw)
In-Reply-To: <6583ed1f-3ea3-c7fd-7e69-1430c8387e54@intel.com>


* Rafael J. Wysocki <rafael.j.wysocki@intel.com> wrote:

> Hi Linus,
> 
> On 11/9/2017 11:38 AM, WANG Chao wrote:
> > Commit 941f5f0f6ef5 (x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo) caused
> > a serious performance issue when reading from /proc/cpuinfo on system
> > with aperfmperf.
> > 
> > For each cpu, arch_freq_get_on_cpu() sleeps 20ms to get its frequency.
> > On a system with 64 cpus, it takes 1.5s to finish running `cat
> > /proc/cpuinfo`, while it previously was done in 15ms.
> 
> Honestly, I'm not sure what to do to address this ATM.
> 
> The last requested frequency is only available in the non-HWP case, so it
> cannot be used universally.

This is a serious regression that needs to be fixed ASAP, because the slowdown is 
utterly ridiculous on a 120 CPU system:

  fomalhaut:~> time cat /proc/cpuinfo  >/dev/null

  real    0m2.689s
  user    0m0.001s
  sys     0m0.007s

Thanks,

	Ingo

  parent reply	other threads:[~2017-11-10  7:25 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-09 10:38 [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again WANG Chao
2017-11-09 16:06 ` Rafael J. Wysocki
2017-11-09 22:30   ` Rafael J. Wysocki
2017-11-10  0:06     ` Rafael J. Wysocki
2017-11-10  4:04       ` WANG Chao
2017-11-10  4:11         ` WANG Chao
2017-11-10 19:11     ` Linus Torvalds
2017-11-10 23:09       ` Rafael J. Wysocki
2017-11-14 22:47         ` Rafael J. Wysocki
2017-11-14 23:02           ` Linus Torvalds
2017-11-14 23:53             ` Thomas Gleixner
2017-11-15  0:04               ` Linus Torvalds
2017-11-15  0:06                 ` Linus Torvalds
2017-11-15  0:30                   ` Rafael J. Wysocki
2017-11-15  0:34                     ` Linus Torvalds
2017-11-15  1:13                       ` [PATCH] x86 / CPU: Always show current CPU frequency in /proc/cpuinfo Rafael J. Wysocki
2017-11-15  8:47                         ` Thomas Gleixner
2017-11-15  9:33                         ` WANG Chao
2017-11-16  0:24                           ` Rafael J. Wysocki
2017-11-16  9:50                             ` WANG Chao
2017-11-16 13:54                               ` Rafael J. Wysocki
2017-11-17  4:27                                 ` WANG Chao
2017-11-17 13:33                                   ` Rafael J. Wysocki
2017-11-15  7:43                     ` [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again Ingo Molnar
2017-11-15  7:54                       ` Greg Kroah-Hartman
2017-11-15 17:27                       ` Linus Torvalds
2017-11-15 18:05                         ` Thomas Gleixner
2017-11-15  8:47                 ` Thomas Gleixner
2017-11-15  0:06               ` Rafael J. Wysocki
2017-11-10  7:25   ` Ingo Molnar [this message]
2017-11-10  9:21     ` WANG Chao

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