Date: Tue, 15 Mar 2011 15:51:53 -0400 From: John Baldwin <jhb@freebsd.org> To: "Jung-uk Kim" <jkim@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Bruce Evans <brde@optusnet.com.au> Subject: Re: svn commit: r219646 - head/sys/x86/isa Message-ID: <201103151551.54196.jhb@freebsd.org> In-Reply-To: <201103151526.14264.jkim@FreeBSD.org> References: <201103142205.p2EM5x6E012664@svn.freebsd.org> <20110316035308.A2598@besplex.bde.org> <201103151526.14264.jkim@FreeBSD.org>
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On Tuesday, March 15, 2011 3:26:11 pm Jung-uk Kim wrote: > Now don't you think we should really kill delay by TSC? ;-) Delay by TSC fixed known deadlocks with the i8254 based DELAY() due to the use of locks. Be careful that you don't re-introduce old bugs. Also, you can use a TSC for DELAY() in cases when it is not safe to use it for the timecounter (if it is not in sync across cores, but is used in a machine with invariant TSCs or where the user knows they won't ever throttle it). Modern Intel CPUs all have invariant TSCs that are more or less in sync across cores, and we should certainly still use the TSC for DELAY() in that case. Even if they aren't in sync (so we can't use it for the timecounter) we should still use the TSC if they are invariant as it is far cheaper than anything else. -- John Baldwin
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