Date: Sat, 28 Jul 2012 20:12:16 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Jim Harris <jim.harris@gmail.com> Cc: "amd64@freebsd.org" <amd64@freebsd.org>, Andriy Gapon <avg@freebsd.org> Subject: Re: Use fences for kernel tsc reads. Message-ID: <20120728171216.GK2676@deviant.kiev.zoral.com.ua> In-Reply-To: <CAJP=Hc8HSh9tsvFhShOP29=o0zV3ngi0gVyx-RQg%2BToCk_TdRA@mail.gmail.com> References: <20120728160202.GI2676@deviant.kiev.zoral.com.ua> <CAJP=Hc8HSh9tsvFhShOP29=o0zV3ngi0gVyx-RQg%2BToCk_TdRA@mail.gmail.com>
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--USf1PyUzamLyyBMw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Jul 28, 2012 at 09:36:43AM -0700, Jim Harris wrote: > On Saturday, July 28, 2012, Konstantin Belousov wrote: >=20 > > Hi, > > > > This was discussed on somewhat unwieldly thread on svn-src@ as a follow= up > > to the commit r238755 which uncovered the problem in the first place. > > > > Below is the commit candidate. It changes the fix in r238755 to use CPU= ID > > instead of rmb(), since rmb() translates to locked operation on i386, > > and experimentation shown that Nehalem's RDTSC can pass LOCK. > > > > Also, I explicitely use LFENCE and MFENCE instead using rmb() and mb(), > > for the same reason that on i386 implementation of *mb() is a locked > > operation instead of fence. > > > > Jim, could you please, recheck that on your machine there is no regress= ion > > in the TSC synchronization test ? > > > Ok. I will do this first thing on Monday. Should I still MFC my patch to > stable-9? Definitely, please merge. I do not think that SMP && !SSE2 is important population for us, and since SMP machines of that kind were definitely multi-socket, I doubt that TSC was synchronized for them anyway. Users will need to disable tsc manually. --USf1PyUzamLyyBMw Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAlAUHXAACgkQC3+MBN1Mb4gh2ACdHZRNWFg6/mRRoCma1QbbXERb E94AoOabrODg9s2idvR24ALDlZCWOxyV =JUhS -----END PGP SIGNATURE----- --USf1PyUzamLyyBMw--
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