linux-kernel - Re: [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation.

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Date:   Mon, 20 Jan 2020 09:19:36 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, nathanl@...ux.ibm.com,
        arnd@...db.de, tglx@...utronix.de, vincenzo.frascino@....com,
        luto@...nel.org, x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org
Subject: Re: [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation.

On Mon, Jan 20, 2020 at 02:56:00PM +0000, Christophe Leroy wrote:
> >Nice!  Much better.
> >
> >It should be tested on more representative hardware, too, but this looks
> >promising alright :-)
> 
> mpc832x (e300c2 core) at 333 MHz:
> 
> Before:
> 
> gettimeofday:    vdso: 235 nsec/call
> clock-gettime-realtime:    vdso: 244 nsec/call
> 
> With the series:
> 
> gettimeofday:    vdso: 271 nsec/call
> clock-gettime-realtime:    vdso: 281 nsec/call

Those are important, and degrade ~15%.  That is acceptable IMO, but do
you see a way to optimise this (later)?

Anyway, excellent results, thanks for your persistence!


Segher