Messages in this thread | | | Subject | Re: [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK | From | Christophe Leroy <> | Date | Thu, 24 Jan 2019 16:58:41 +0100 |
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Le 24/01/2019 à 16:01, Christophe Leroy a écrit : > > > Le 24/01/2019 à 10:43, Christophe Leroy a écrit : >> >> >> On 01/24/2019 01:06 AM, Michael Ellerman wrote: >>> Christophe Leroy <christophe.leroy@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 the 83xx, I have a slight improvment:
Without the serie:
root@vgoippro:~# ./null_syscall 921.44 ns 307.15 cycles
With the serie:
root@vgoippro:~# ./null_syscall 918.78 ns 306.26 cycles
Christophe
>> >>> >>> 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. >
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