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From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Arnd Bergmann <arnd@arndb.de>,
	Segher Boessenkool <segher@kernel.crashing.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Andy Lutomirski <luto@kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>
Subject: Re: Surprising code generated for vdso_read_begin()
Date: Wed, 19 Feb 2020 09:45:45 +0100	[thread overview]
Message-ID: <305fcee5-2e1b-ea4d-9a2a-a0e8034d40a8@c-s.fr> (raw)
In-Reply-To: <CAK8P3a11wX1zJ+TAacDTkYsrzvfdVmNrcB6OC23aFvCxF57opQ@mail.gmail.com>



Le 16/02/2020 à 19:10, Arnd Bergmann a écrit :
> On Sat, Jan 11, 2020 at 12:33 PM Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
>>
>> On Fri, Jan 10, 2020 at 07:45:44AM +0100, Christophe Leroy wrote:
>>> Le 09/01/2020 à 21:07, Segher Boessenkool a écrit :
>>>> It looks like the compiler did loop peeling.  What GCC version is this?
>>>> Please try current trunk (to become GCC 10), or at least GCC 9?
>>>
>>> It is with GCC 5.5
>>>
>>> https://mirrors.edge.kernel.org/pub/tools/crosstool/ doesn't have more
>>> recent than 8.1
>>
>> Arnd, can you update the tools?  We are at 8.3 and 9.2 now :-)  Or is
>> this hard and/or painful to do?
> 
> To follow up on this older thread, I have now uploaded 6.5, 7.5, 8.3 and 9.2
> binaries, as well as a recent 10.0 snapshot.
> 

Thanks Arnd,

I have built the VDSO with 9.2, I get less performant result than with 
8.2 (same performance as with 5.5).

After a quick look, I see:
- Irrelevant NOPs to align loops and stuff, allthough -mpcu=860 should 
avoid that.
- A stack frame is set for saving r31 in __c_kernel_clock_gettime. GCC 
8.1 don't need that, all VDSO functions are frameless with 8.1

Christophe

  reply	other threads:[~2020-02-19  8:45 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-23 14:31 [RFC PATCH v2 00/10] powerpc/32: switch VDSO to C implementation Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 01/10] lib: vdso: ensure all arches have 32bit fallback Christophe Leroy
2019-12-24  2:07   ` Andy Lutomirski
2020-01-10 20:56     ` Thomas Gleixner
2020-01-10 21:02       ` Andy Lutomirski
2019-12-30 12:27   ` Arnd Bergmann
2020-01-02 11:29     ` Arnd Bergmann
2020-01-09 15:43       ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 02/10] lib: vdso: move call to fallback out of common code Christophe Leroy
2019-12-24  2:24   ` Andy Lutomirski
2019-12-24 11:41     ` christophe leroy
2019-12-24 12:09       ` Andy Lutomirski
2019-12-23 14:31 ` [RFC PATCH v2 03/10] lib: vdso: Change __cvdso_clock_gettime/getres_common() to __cvdso_clock_gettime/getres() Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch Christophe Leroy
2019-12-24  2:27   ` Andy Lutomirski
2019-12-24 11:53     ` christophe leroy
2019-12-24 12:15       ` Andy Lutomirski
2019-12-24 12:41         ` Andy Lutomirski
2019-12-24 14:46         ` Segher Boessenkool
2019-12-23 14:31 ` [RFC PATCH v2 05/10] lib: vdso: inline do_hres() Christophe Leroy
2019-12-24  2:29   ` Andy Lutomirski
2019-12-30 12:07   ` Arnd Bergmann
2020-01-10 21:07     ` Thomas Gleixner
2020-01-11  9:06       ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 06/10] lib: vdso: make do_coarse() return 0 Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 07/10] lib: vdso: don't use READ_ONCE() in __c_kernel_time() Christophe Leroy
2019-12-24  1:58   ` Andy Lutomirski
2019-12-24 11:12     ` christophe leroy
2019-12-24 12:04       ` Andy Lutomirski
2020-01-10 21:12   ` Thomas Gleixner
2020-01-11  8:05     ` Christophe Leroy
2020-01-11 11:07       ` Thomas Gleixner
2020-01-13  6:52         ` Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 08/10] lib: vdso: Avoid duplication in __cvdso_clock_getres() Christophe Leroy
2019-12-24  1:59   ` Andy Lutomirski
2019-12-23 14:31 ` [RFC PATCH v2 09/10] powerpc/vdso32: inline __get_datapage() Christophe Leroy
2019-12-23 14:31 ` [RFC PATCH v2 10/10] powerpc/32: Switch VDSO to C implementation Christophe Leroy
2020-01-09 17:52 ` Surprising code generated for vdso_read_begin() Christophe Leroy
2020-01-09 20:07   ` Segher Boessenkool
2020-01-10  6:45     ` Christophe Leroy
2020-01-11 11:33       ` Segher Boessenkool
2020-02-16 18:10         ` Arnd Bergmann
2020-02-19  8:45           ` Christophe Leroy [this message]
2020-02-19  9:52             ` Arnd Bergmann
2020-02-19 13:08               ` Segher Boessenkool

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