linux-kernel - Re: [PATCH 6/8] cleanup __vdso

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Date:	Sun, 02 Feb 2014 07:43:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	stefani@...bold.net, 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
CC:	Martin.Runge@...de-schwarz.com, Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH 6/8] cleanup __vdso_gettimeofday

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 *)

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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