Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754051AbZCTH1i (ORCPT ); Fri, 20 Mar 2009 03:27:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751807AbZCTH1Z (ORCPT ); Fri, 20 Mar 2009 03:27:25 -0400 Received: from fg-out-1718.google.com ([72.14.220.157]:3180 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750782AbZCTH1Y (ORCPT ); Fri, 20 Mar 2009 03:27:24 -0400 Message-ID: <49C34558.6030006@monstr.eu> Date: Fri, 20 Mar 2009 08:27:20 +0100 From: Michal Simek Reply-To: monstr@monstr.eu User-Agent: Thunderbird 2.0.0.17 (X11/20081001) MIME-Version: 1.0 To: John Stultz CC: Thomas Gleixner 1 , LKML , john.williams@petalogix.com Subject: Re: [PATCH 08/57] microblaze_v7: Interrupt handling, timer support, selfmod code References: <1237408284-8674-1-git-send-email-monstr@monstr.eu> <0168f03c96e9479ede695a9859c8a0691baa8ef3.1237407249.git.monstr@monstr.eu> <4b5aee01d11fc790c7842838ea63a82ee3273003.1237407249.git.monstr@monstr.eu> <5f8b2a60496983f572ef6d3b4e2f986c167a8336.1237407249.git.monstr@monstr.eu> <20fd42a1e8837c7352d35d157aa3393e88152c32.1237407249.git.monstr@monstr.eu> <49C2AB09.9040300@monstr.eu> <1237515861.7106.215.camel@jstultz-laptop> In-Reply-To: <1237515861.7106.215.camel@jstultz-laptop> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7865 Lines: 244 Hi John S, > On Thu, 2009-03-19 at 22:47 +0100, Thomas Gleixner wrote: >> On Thu, 19 Mar 2009, Michal Simek wrote: >>> And the second question is about shift and rating values. >>> I wrote one message in past http://lkml.org/lkml/2009/1/11/291 >>> Here is the important of part of that message. >>> >>> ... >>> >>> And the second part is about shift and rating values. Rating is >>> describe(linux/clocksource.h) and seems to me that should be >>> corresponded with CONFIG_HZ value,right? > > Not sure where the idea of correspondence w/ CONFIG_HZ came from. The > rating value just provides a relative ordering of preferences between > possible clocksources. Since different hardware may have a number of > different clocksources available, we just need to have a method of > selecting a preferred clocksource, and the rating value is used for > that. > > The guide in linux/clocksource.h is just a guide. Most arches, which > only have one or two clocksource options probably won't need much care, > and a rating of 200 or 300 will probably suffice. Or if there really > isn't any option about it and there is only one which is a must-use > clocksource, 400. ok. That mean that for my case (only one clocksource) I should set rating to 400 - I have one clocksource and is perfect for me. > > >>> And I found any explanation of shift value -> max value for equation >>> (2-5) * freq << shift / NSEC_PER_SEC should be for my case still 32bit >>> number, where (2-5s) are because of NTP >> @John, can you explain the shift vlaue please ? > > The shift value is a bit more difficult to explain. The algorithm you > describe above is used by sparc to generate shift, and I think it will > work, but may not be optimal. > > This question comes up over and over, so I figured I should sit down and > really solve it. > > Basically the constraint is you want to calculate a mult value using the > highest shift possible. However we have to be careful not to overflow > 64bits when we multiply ~5second worth of cycles times the mult value. > > So I finally put this down into code and here it is. No promises that it > is 100% right, but from my simple test examples it worked ok. OK. Please check my case of that value. MB can run from 5Mhz till 150MHz I think. I need generic approach that's why I have to calculate with max value (150MHz). My timer can tick on that freq too. (There is no different time bases in HW). I need to find out how many ticks takes ~5s. 150MHz means that I need for 1sec 150 000 000 timer ticks. One tick takes 1/150MHz = ~6-7ns - in the best case I can recognize and set 6-7ns (this is only theoretical value because of overhead) ~5s takes 750 000 000 ticks = 0x2CB4 1780. And I have 32bit counter. That my question is how big could be a shift of value above till overflow. 0x2CB4 1780 << shift not exceed 0xffff ffff ffff ffff. Here is that table for my case shift 0 = 0x2CB4 1780 1 = 0x5968 2F00 2 = 0xB2D0 5E00 3 = 0x1 65A0 BC00 4 = 0x2 CB41 7800 5 = 0x5 9682 F000 6 = 0xB 2D05 E000 7 = 0x16 5A0B C000 >From first value I can tell that I can shift that value with 32 + 3 => 35 is the first shift with overflow 64bit. Am I right? If yes, I haven't found that big value in any arch. For example avr has shift 16, rating 50 (arch/avr32/kernel/time.c) (BTW: Sets time from 2007 too) And the next my question is about difference in clocksource and clock event value. Situation is the same. Is it mean that I should set the same rating and shift value for both. (It doesn't matter if I use one or two timer -> they are the same). And about high resolution timer. I can recognize in the best case ~6-7ns. That mean that measuring values around 100-200ns make sense and should work. Could I use it? Thanks, Michal > Let me know if it helps. > > thanks > -john > > > Add helper functions to calculate ideal clocksource shift values given > its frequency (either hz or khz). Lightly tested, use with care. > Also fixes a few old-old-old timesource (well, timsource) references my > find and replace attempts failed on. > > Signed-off-by: John Stultz > > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h > index f88d32f..9ef062d 100644 > --- a/include/linux/clocksource.h > +++ b/include/linux/clocksource.h > @@ -116,7 +116,7 @@ extern struct clocksource *clock; /* current clocksource */ > * @khz: Clocksource frequency in KHz > * @shift_constant: Clocksource shift factor > * > - * Helper functions that converts a khz counter frequency to a timsource > + * Helper functions that converts a khz counter frequency to a clocksource > * multiplier, given the clocksource shift value > */ > static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant) > @@ -142,7 +142,7 @@ static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant) > * @shift_constant: Clocksource shift factor > * > * Helper functions that converts a hz counter > - * frequency to a timsource multiplier, given the > + * frequency to a clocksource multiplier, given the > * clocksource shift value > */ > static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) > @@ -162,6 +162,10 @@ static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) > return (u32)tmp; > } > > +extern u32 clocksource_khz2shift(u32 freq_khz); > +extern u32 clocksource_hz2shift(u32 freq_hz); > + > + > /** > * clocksource_read: - Access the clocksource's current cycle value > * @cs: pointer to clocksource being read > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index ca89e15..0a2538d 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -212,6 +212,83 @@ static void clocksource_check_watchdog(struct clocksource *cs) > static inline void clocksource_resume_watchdog(void) { } > #endif > > + > +/* Maximum seconds worth of cycles we consider valid */ > +#define MAX_SEC_OF_CYCLES 5ULL > + > +/** > + * clocksource_khz2shift - calculates shift from khz > + * @freq_khz: Clocksource frequency in KHz > + * > + * Helper functions that converts a khz counter > + * frequency to a clocksource shift. > + */ > +u32 clocksource_khz2shift(u32 freq_khz) > +{ > + s32 shift = 32; > + u32 mult; > + > + while (1) { > + s64 tmp; > + u64 cycles; > + mult = clocksource_khz2mult(freq_khz, shift); > + > + cycles = (u64)freq_khz*1000*MAX_SEC_OF_CYCLES; > + tmp = (cycles * mult) >> shift; > + > + tmp = (MAX_SEC_OF_CYCLES*NSEC_PER_SEC) - tmp; > + if (tmp < 0) > + tmp = -tmp; > + > + /* if we are witin one mult unit, we're good */ > + if (tmp < cycles>>shift) > + break; > + > + shift--; > + if (shift < 1) > + BUG(); > + } > + return shift; > +} > + > +/** > + * clocksource_hz2shift - calculates shift from hz > + * @freq_hz: Clocksource frequency in Hz > + * > + * Helper functions that converts a hz counter > + * frequency to a clocksource shift. > + */ > + > +u32 clocksource_hz2shift(u32 freq_hz) > +{ > + s32 shift = 32; > + u32 mult; > + > + while (1) { > + s64 tmp; > + u64 cycles; > + mult = clocksource_hz2mult(freq_hz, shift); > + > + cycles = (u64)freq_hz*MAX_SEC_OF_CYCLES; > + tmp = (cycles * mult) >> shift; > + > + tmp = MAX_SEC_OF_CYCLES*NSEC_PER_SEC - tmp; > + if (tmp < 0) > + tmp = -tmp; > + > + /* if we are witin one mult unit, we're good */ > + if (tmp < cycles>>shift) > + break; > + > + shift--; > + if (shift < 1) > + BUG(); > + } > + return shift; > +} > + > + > + > /** > * clocksource_resume - resume the clocksource(s) > */ > > -- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/