From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Wienand Date: Mon, 13 Oct 2003 02:11:52 +0000 Subject: Re: [PATCH_TAKE_2] now < last_tick problem MIME-Version: 1 Content-Type: multipart/mixed; boundary="KsGdsel6WgEHnImy" Message-Id: List-Id: References: In-Reply-To: To: linux-ia64@vger.kernel.org --KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Oct 10, 2003 at 09:42:35AM -0700, David Mosberger wrote: > I think the source of the probem is that we consider the value > returned by get_offset() to be valid EVEN when read_seqretry() returns > 1. Because of that, we'll end up updating last_nsec_offset with a > potentialy bad value. Well, to my eyes the use of the xtime_lock in do_gettimeofday() looks OK, but I guess what you are saying is that the message is moot -- xtime_lock protects everything itc_get_offset() needs, and do_gettimeofday() has a read lock on xtime_lock and so reads the offset again if something was updated underneath it. -i --KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="time.c.nomsg.diff" ===== arch/ia64/kernel/time.c 1.35 vs edited ===== --- 1.35/arch/ia64/kernel/time.c Wed Oct 8 12:53:38 2003 +++ edited/arch/ia64/kernel/time.c Mon Oct 13 11:54:05 2003 @@ -65,8 +65,11 @@ } /* - * Return the number of nano-seconds that elapsed since the last update to jiffy. The - * xtime_lock must be at least read-locked when calling this routine. + * Return the number of nano-seconds that elapsed since the last + * update to jiffy. It is quite possible that the timer interrupt + * will interrupt this and result in a race for any of jiffies, + * wall_jiffies or itm_next. Thus, the xtime_lock must be at least + * read-locked when calling this routine. */ unsigned long itc_get_offset (void) @@ -77,11 +80,6 @@ last_tick = (cpu_data(TIME_KEEPER_ID)->itm_next - (lost + 1)*cpu_data(TIME_KEEPER_ID)->itm_delta); - if (unlikely((long) (now - last_tick) < 0)) { - printk(KERN_ERR "CPU %d: now < last_tick (now=0x%lx,last_tick=0x%lx)!\n", - smp_processor_id(), now, last_tick); - return last_nsec_offset; - } elapsed_cycles = now - last_tick; return (elapsed_cycles*local_cpu_data->nsec_per_cyc) >> IA64_NSEC_PER_CYC_SHIFT; } --KsGdsel6WgEHnImy--