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Date: Sun, 02 Feb 2014 17:02:52 +0100 From: Stefani Seibold <stefani@...bold.net> To: "H. Peter Anvin" <hpa@...or.com> Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, ak@...ux.intel.com, aarcange@...hat.com, john.stultz@...aro.org, luto@...capital.net, xemul@...allels.com, gorcunov@...nvz.org, andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com, Andreas.Brief@...de-schwarz.com Subject: Re: [PATCH 6/8] cleanup __vdso_gettimeofday On Sun, 2014-02-02 at 07:43 -0800, H. Peter Anvin wrote: > Even reading the timezone via gettimeofday is the uncommon case... never mind only the timezome. Whatever you do please don't slow down the common case. > > On February 2, 2014 3:27:13 AM PST, stefani@...bold.net wrote: > >From: Stefani Seibold <stefani@...bold.net> > > > >This patch do a little cleanup for the __vdso_gettimeofday() function. > > > >It kick out an unneeded ret local variable and makes the code faster if > >only the timezone is needed. > > > >Signed-off-by: Stefani Seibold <stefani@...bold.net> > >--- > > arch/x86/vdso/vclock_gettime.c | 7 ++----- > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > >diff --git a/arch/x86/vdso/vclock_gettime.c > >b/arch/x86/vdso/vclock_gettime.c > >index 743f277..bf969a0 100644 > >--- a/arch/x86/vdso/vclock_gettime.c > >+++ b/arch/x86/vdso/vclock_gettime.c > >@@ -259,13 +259,12 @@ int clock_gettime(clockid_t, struct timespec *) > > > >notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone > >*tz) > > { > >- long ret = VCLOCK_NONE; > >- > > if (likely(tv != NULL)) { > > BUILD_BUG_ON(offsetof(struct timeval, tv_usec) != > > offsetof(struct timespec, tv_nsec) || > > sizeof(*tv) != sizeof(struct timespec)); > >- ret = do_realtime((struct timespec *)tv); > >+ if (do_realtime((struct timespec *)tv) == VCLOCK_NONE) > >+ return vdso_fallback_gtod(tv, tz); > > tv->tv_usec /= 1000; > > } > > if (unlikely(tz != NULL)) { > >@@ -274,8 +273,6 @@ notrace int __vdso_gettimeofday(struct timeval *tv, > >struct timezone *tz) > > tz->tz_dsttime = gtod->sys_tz.tz_dsttime; > > } > > > >- if (ret == VCLOCK_NONE) > >- return vdso_fallback_gtod(tv, tz); > > return 0; > > } > > int gettimeofday(struct timeval *, struct timezone *) > I don't see where i slow down the common case! It is exactly the same behaviour as the original code. Only in the uncommon case where the tv == NULL and tz != NULL is a bit faster. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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