linux-kernel - Re: 3.10.9: kmemleak disables all CPUs except CPU0

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Date:	Mon, 02 Sep 2013 17:51:17 +0200
From:	Martin MOKREJŠ <mmokrejs@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Max Filippov <jcmvbkbc@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 3.10.9: kmemleak disables all CPUs except CPU0



Catalin Marinas wrote:
> On Mon, Sep 02, 2013 at 04:44:52PM +0100, Max Filippov wrote:
>> On Mon, Sep 2, 2013 at 7:31 PM, Catalin Marinas <catalin.marinas@....com> wrote:
>>> On 31 August 2013 14:35, Martin MOKREJŠ <mmokrejs@...il.com> wrote:
>>>>   never realized that my CPUs are gone if I compile into kernel kmemleak.
>>>> Is that really the aim?
>>>>
>>>> CONFIG_HAVE_DEBUG_KMEMLEAK=y
>>>> CONFIG_DEBUG_KMEMLEAK=y
>>>> CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE=400
>>>> # CONFIG_DEBUG_KMEMLEAK_TEST is not set
>>>> # CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF is not set
>>>>
>>>> 1.  Why isn't there /sys/devices/system/cpu/cpu0/online file?
>>>> Does not matter if it contains 0 or 1. It just should exist.
>>>
>>> I can't really see how kmemleak would do this, maybe other config
>>> options that get set/cleared in the process of selecting kmemleak. Can
>>
>> Seems to be kmemcheck: from arch/x86/mm/kmemcheck/kmemcheck.c:
>>
>> int __init kmemcheck_init(void)
>> {
>> #ifdef CONFIG_SMP
>>         /*
>>          * Limit SMP to use a single CPU. We rely on the fact that this code
>>          * runs before SMP is set up.
>>          */
>>         if (setup_max_cpus > 1) {
>>                 printk(KERN_INFO
>>                         "kmemcheck: Limiting number of CPUs to 1.\n");
>>                 setup_max_cpus = 1;
>>         }
>> #endif
> 
> Ah, ok, not my problem then ;)


Fine, so would somebody please update the help text accessible in "menuconfig"
for this entry? It should be clear that it has a huge performance impact if enabled.
And, by compiling in it is enabled by default.

Thank you
Martin
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