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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK
Date: Thu, 24 Jan 2019 12:06:45 +1100	[thread overview]
Message-ID: <87y37ax3ru.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <2e700e1c-5bd9-652e-b535-68a89dd703a1@c-s.fr>

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?

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?

cheers

  reply	other threads:[~2019-01-24  1:08 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-12  9:55 [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 01/10] powerpc/irq: use memblock functions returning virtual address Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 02/10] book3s/64: avoid circular header inclusion in mmu-hash.h Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 03/10] powerpc: Only use task_struct 'cpu' field on SMP Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 04/10] powerpc: Prepare for moving thread_info into task_struct Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 05/10] powerpc: Activate CONFIG_THREAD_INFO_IN_TASK Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 06/10] powerpc: regain entire stack space Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 07/10] powerpc: 'current_set' is now a table of task_struct pointers Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 08/10] powerpc/32: Remove CURRENT_THREAD_INFO and rename TI_CPU Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 09/10] powerpc/64: Remove CURRENT_THREAD_INFO Christophe Leroy
2019-01-12  9:55 ` [PATCH v13 10/10] powerpc: clean stack pointers naming Christophe Leroy
2019-01-19 10:23 ` [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK Michael Ellerman
2019-01-19 17:21   ` LEROY Christophe
2019-01-23 23:10     ` Michael Ellerman
2019-01-22 19:42   ` Christophe Leroy
2019-01-24  0:59     ` Michael Ellerman
2019-01-24 15:08       ` Christophe Leroy
2019-01-23 10:04 ` Christophe Leroy
2019-01-24  1:06   ` Michael Ellerman [this message]
2019-01-24  9:43     ` Christophe Leroy
2019-01-24 15:01       ` Christophe Leroy
2019-01-24 15:58         ` Christophe Leroy
2019-01-25  7:00           ` Gabriel Paubert

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