lkml.org 
[lkml]   [2016]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: x86_64 Compiler Output Kernel Bloat v4.4
From
On 1/19/16, Jiri Olsa <jolsa@redhat.com> wrote:
> On Mon, Jan 18, 2016 at 02:45:14PM -0700, Jeff Merkey wrote:
>
> SNIP
>
>> > 0xffffffffa073e019 E8C2579FE0 call
>> > touch_softlockup_watchdog_sync
>> > 0xffffffffa073e01e E87D2B9BE0 call clocksource_touch_watchdog
>> > 0xffffffffa073e023 E8F8099AE0 call rcu_cpu_stall_reset
>> > 0xffffffffa073e028 E893579FE0 call touch_nmi_watchdog
>> > 0xffffffffa073e02d 5D pop rbp
>> > 0xffffffffa073e02e 6690 data16
>> > 0xffffffffa073e030 C3 ret
>> > 0xffffffffa073e031 6666666666662E0F1F840000000000 nop cs:WORD PTR
>> > [rax+rax]=0x0000
>> > mdb|mdb:
>> > 0xffffffffa073e040 0F1F440000 nop DWORD PTR [rax+rax]=0x0 <<
>> > 0xffffffffa073e045 55 push rbp
>> > 0xffffffffa073e046 4889E5 mov rbp,rsp
>> > 0xffffffffa073e049 4157 push r15
>> > 0xffffffffa073e04b 4156 push r14
>> > 0xffffffffa073e04d 4989FE mov r14,rdi
>> > 0xffffffffa073e050 4155 push r13
>> > (0)> g
>> >
>> > Jeff
>> >
>>
>> I think xor eax,eax is a lot shorter and fewer bytes.
>
> that 5 byte nop gets replaced by call instruction once the
> function trace is enabled
>
> explained in CONFIG_FUNCTION_TRACER option doc:
>
>
> config FUNCTION_TRACER
> bool "Kernel Function Tracer"
> depends on HAVE_FUNCTION_TRACER
> select KALLSYMS
> select GENERIC_TRACER
> select CONTEXT_SWITCH_TRACER
> help
> Enable the kernel to trace every kernel function. This is done
> by using a compiler feature to insert a small, 5-byte
> No-Operation
> instruction at the beginning of every kernel function, which NOP
> sequence is then dynamically patched into a tracer call when
> tracing is enabled by the administrator. If it's runtime disabled
> (the bootup default), then the overhead of the instructions is
> very
> small and not measurable even in micro-benchmarks.
>
> jirka
>

Takes up a lot of space since linux has so monay small functions.
Someone sent me the ftrace stuff and I looked over it. Thanks.

Jeff

\
 
 \ /
  Last update: 2016-01-19 16:41    [W:0.057 / U:1.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site