linux-kernel - Re: [PATCHv8 02/34] lib/vdso: make do_hres and do_coarse as __always

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Message-ID: <e74a63cb-5248-4473-81a7-d1b2f959ec7a@arm.com>
Date:   Fri, 10 Jan 2020 11:47:43 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCHv8 02/34] lib/vdso: make do_hres and do_coarse as
 __always_inline



On 1/10/20 11:42 AM, Thomas Gleixner wrote:
> Vincenzo Frascino <vincenzo.frascino@....com> writes:
>> On 11/12/19 1:26 AM, Dmitry Safonov wrote:
>>> +» » vd·=·&vd[CS_HRES_COARSE];
>>> +out_hres:
>>> +» » return·do_hres(vd,·clock,·ts);
>>> » }·else·if·(msk·&·VDSO_COARSE)·{
>>> » » do_coarse(&vd[CS_HRES_COARSE],·clock,·ts);
>>> » » return·0;
>>> » }·else·if·(msk·&·VDSO_RAW)·{
>>> -» » return·do_hres(&vd[CS_RAW],·clock,·ts);
>>> +» » vd·=·&vd[CS_RAW];
>>> +» » /*·goto·allows·to·avoid·extra·inlining·of·do_hres.·*/
>>> +» » goto·out_hres;
>>
>> What is the performance impact of "goto out_hres"?
> 
> On x86 it's invisible at least in my limited testing.

On arm64 as well based on mine as well. Shall we keep the code more readable
here (without goto)?

> 
> Thanks,
> 
>         tglx
> 

-- 
Regards,
Vincenzo