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Date:   Fri, 21 Oct 2022 10:21:12 -0700
From:   Kees Cook <kees@kernel.org>
To:     Alexander Potapenko <glider@google.com>,
        youling 257 <youling257@gmail.com>
CC:     Marco Elver <elver@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Biggers <ebiggers@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 18/43] instrumented.h: add KMSAN support
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On October 21, 2022 10:02:05 AM PDT, Alexander Potapenko <glider@google=2Ec=
om> wrote:
>On Fri, Oct 21, 2022 at 8:19 AM youling 257 <youling257@gmail=2Ecom> wrot=
e:
>
>> CONFIG_DEBUG_INFO=3Dy
>> CONFIG_AS_HAS_NON_CONST_LEB128=3Dy
>> # CONFIG_DEBUG_INFO_NONE is not set
>> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=3Dy
>> # CONFIG_DEBUG_INFO_DWARF4 is not set
>> # CONFIG_DEBUG_INFO_DWARF5 is not set
>> # CONFIG_DEBUG_INFO_REDUCED is not set
>> # CONFIG_DEBUG_INFO_COMPRESSED is not set
>> # CONFIG_DEBUG_INFO_SPLIT is not set
>> # CONFIG_DEBUG_INFO_BTF is not set
>> # CONFIG_GDB_SCRIPTS is not set
>>
>> perf top still no function name=2E
>>
>Will it help if you disable CONFIG_RANDOMIZE_BASE?
>(if it doesn't show the symbols, at least we'll be able to figure out the
>offending function by running nm)

Is KALLSYMS needed?

>
>
>>
>> 12=2E90%  [kernel]              [k] 0xffffffff833dfa64
>>      3=2E78%  [kernel]              [k] 0xffffffff8285b439
>>      3=2E61%  [kernel]              [k] 0xffffffff83370254
>>      2=2E32%  [kernel]              [k] 0xffffffff8337025b
>>      1=2E88%  bluetooth=2Edefault=2Eso  [=2E] 0x000000000000d09d
>>
>> 2022-10-21 15:37 GMT+08:00, Marco Elver <elver@google=2Ecom>:
>> > On Thu, 20 Oct 2022 at 23:39, youling 257 <youling257@gmail=2Ecom> wr=
ote:
>> >>
>> >> PerfTop:    8253 irqs/sec  kernel:75=2E3%  exact: 100=2E0% lost: 0/0=
 drop:
>> >> 0/17899 [4000Hz cycles],  (all, 8 CPUs)
>> >>
>> -----------------------------------------------------------------------=
---------------------------------------------------------------------------=
-------------------------------------------------------------
>> >>
>> >>     14=2E87%  [kernel]              [k] 0xffffffff941d1f37
>> >>      6=2E71%  [kernel]              [k] 0xffffffff942016cf
>> >>
>> >> what is 0xffffffff941d1f37?
>> >
>> > You need to build with debug symbols:
>> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=3Dy
>> >
>> > Then it'll show function names=2E
>> >
>> >> 2022-10-21 14:16 GMT+08:00, Marco Elver <elver@google=2Ecom>:
>> >> > On Thu, 20 Oct 2022 at 22:55, youling 257 <youling257@gmail=2Ecom>
>> wrote:
>> >> >>
>> >> >> How to use perf tool?
>> >> >
>> >> > The simplest would be to try just "perf top" - and see which kerne=
l
>> >> > functions consume most CPU cycles=2E I would suggest you compare b=
oth
>> >> > kernels, and see if you can spot a function which uses more cycles=
% in
>> >> > the problematic kernel=2E
>> >> >
>> >
>>
>
>


--=20
Kees Cook