Date: Fri, 3 Jun 2011 07:50:37 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Jung-uk Kim <jkim@freebsd.org>, Andriy Gapon <avg@freebsd.org> Subject: Re: [RFC] Enabling invariant TSC timecounter on SMP Message-ID: <201106030750.37264.jhb@freebsd.org> In-Reply-To: <4DE8794B.60100@FreeBSD.org> References: <201105241356.45543.jkim@FreeBSD.org> <201106011655.51233.jkim@FreeBSD.org> <4DE8794B.60100@FreeBSD.org>
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On Friday, June 03, 2011 2:03:55 am Andriy Gapon wrote: > > Consecutive RDTSCs used on a same CPU is always incremental but we > > cannot 100% guarantee that on two cores, even if TSC is derived from > > the same clock. I am hoping at least latency difference (I believe > > it's about few tens of cycles max) is "eaten up" by lowering > > resolution. It's not perfect but it's better than serialization > > (Linux) or heuristics (OpenSolaris), just because there are few rare > > conditions to consider. Thoughts? > > I am still not sure which case this code should solve. > > Thread T1: x1 = rdtsc() on CPU1; > Thread T1: x2 = rdtsc() on CPU2; > x2 < x1 ? > Or? Yes, that can happen. -- John Baldwin
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