Le 24/01/2019 à 10:43, Christophe Leroy a écrit :
On 01/24/2019 01:06 AM, Michael Ellerman wrote:
Christophe Leroy <christophe.le...@c-s.fr> writes:
Le 12/01/2019 à 10:55, Christophe Leroy a écrit :
The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK
which
moves the thread_info into task_struct.
Moving thread_info into task_struct has the following advantages:
- It protects thread_info from corruption in the case of stack
overflows.
- Its address is harder to determine if stack addresses are
leaked, making a number of attacks more difficult.
I ran null_syscall and context_switch benchmark selftests and the result
is surprising. There is slight degradation in context_switch and a
significant one on null_syscall:
Without the serie:
~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp
55542
55562
55564
55562
55568
...
~# ./null_syscall
2546.71 ns 336.17 cycles
With the serie:
~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp
55138
55142
55152
55144
55142
~# ./null_syscall
3479.54 ns 459.30 cycles
So 0,8% less context switches per second and 37% more time for one
syscall ?
Any idea ?
What platform is that on?
It is on the 8xx
On 64-bit we have to turn one mtmsrd into two and that's obviously a
slow down. But I don't see that you've done anything similar in 32-bit
code.
I assume it's patch 8 that causes the slow down?
I have not digged into it yet, but why patch 8 ?
The increase of null_syscall duration happens with patch 5 when we
activate CONFIG_THREAD_INFO_IN_TASK.
Christophe