From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: clock_gettime.2: _COARSE clocks are not always faster... Date: Mon, 18 Apr 2016 16:23:24 +0100 Message-ID: <5714FBEC.80209@gmail.com> References: <87k2k67ml4.fsf@rasmusvillemoes.dk> <5714F972.6080603@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <5714F972.6080603-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Rasmus Villemoes Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org List-Id: linux-man@vger.kernel.org On 04/18/2016 04:12 PM, Michael Kerrisk (man-pages) wrote: > Hello Rasmus, >=20 > On 04/09/2016 05:50 PM, Rasmus Villemoes wrote: >> Hi Michael >> >> The other day, I was curious how the vdso was implemented on ppc, an= d I >> noted that neither ppc32 or ppc64 handle the _COARSE versions of >> CLOCK_{REALTIME,MONOTONIC} in the vdso, so they fall back to an actu= al >> syscall. And sure enough, measuring CLOCK_MONOTONIC >> vs. CLOCK_MONOTONIC_COARSE shows that the latter has three times as = much >> overhead as the former. >> >> Whether it's worth adding a note to the man page is up to you. >=20 > I think it's useful to do so. For both *COARSE flags, I added: >=20 > [[ > Requires per-architecture support, and probably also architecture sup= port > for this flag in the vdso(7). > ]] And in the PowerPC sections of vdso(7), I added: The CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE clocks are not supported by the __kernel_clock_getres and __ker=E2= =80=90 nel_clock_gettime interfaces; the kernel falls back to the real system call. Cheers, Michael --=20 Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html