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 16:01:59 +0100 |
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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 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
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