Date: Wed, 17 Apr 2013 01:04:39 +0300 From: Alexander Motin <mav@FreeBSD.org> To: freebsd-hackers@FreeBSD.org Subject: Synchronizing TSC Message-ID: <516DCAF7.20400@FreeBSD.org>
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Hi. Recently I've got 6-core/12-thread system on Sandy Bridge-E Core i7-3930K CPU and was unpleasantly surprised to see that TSCs are not synchronized there. While all 11 APs were synchronized, BSP was far behind them. Since it is single-socket system, I don't know any good reason for such behavior except some BIOS bug. But I've recalled that somewhere was some discussions about possible TSC synchronization. I've implemented patch below that allows to adjust TSC values of BSPs to AP's one on boot using CPU MSRs, hoping that they should not diverge after that: http://people.freebsd.org/~mav/tsc_adj2.patch I don't know very much about all different TSC hardware to predict when it is safe to enable the functionality, but at least on my system being enabled via loader tunable it seems working well. Comments? -- Alexander Motin
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