From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Walker Date: Wed, 27 May 2009 16:25:25 +0000 Subject: Re: [PATCH] sched: Support current clocksource handling in Message-Id: <1243441525.28705.19.camel@desktop> List-Id: References: <20090526061532.GD9188@linux-sh.org> <63386a3d0905260731m655bfee3q82a6f52d71fa3cef@mail.gmail.com> <1243348681.23657.14.camel@twins> <20090526230855.GA27218@linux-sh.org> <20090527001543.GA8493@linux-sh.org> In-Reply-To: <20090527001543.GA8493@linux-sh.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Paul Mundt Cc: Thomas Gleixner , Peter Zijlstra , Linus Walleij , Ingo Molnar , Andrew Victor , Haavard Skinnemoen , Andrew Morton , linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk, John Stultz On Wed, 2009-05-27 at 09:15 +0900, Paul Mundt wrote: > unsigned long long __attribute__((weak)) sched_clock(void) > { > + /* > + * Use the current clocksource when it becomes available later in > + * the boot process, and ensure that it is usable for sched_clock(). > + */ > + if (clock && (clock->flags & CLOCK_SOURCE_USE_FOR_SCHED_CLOCK)) > + return cyc2ns(clock, clocksource_read(clock)); > + > + /* Otherwise just fall back on jiffies */ > return (unsigned long long)(jiffies - INITIAL_JIFFIES) Do we really need all this complexity in a fast path? the jiffies clocksource is static and always ready. Could we instead remove the usage of "clock" and create a new pointer called "sched_clocksource" and initialize it to the jiffies clock, and allow the clocksource management code to update that new pointer based on the CLOCK_SOURCE_USE_FOR_SCHED_CLOCK flag when new clocksources are registered/removed/marked unstable etc.. that would eliminate all the code in sched_clock except one line, unsigned long long __attribute__((weak)) sched_clock(void) { return cyc2ns(sched_clocksource, clocksource_read(sched_clocksource)); } Daniel