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Message-ID: <57C9024A16AD2D4C97DC78E552063EA308329139@orsmsx505.amr.corp.intel.com> Date: Mon, 4 Aug 2008 15:10:40 -0700 From: "Luck, Tony" <tony.luck@...el.com> To: David Miller <davem@...emloft.net> CC: "nacc@...ibm.com" <nacc@...ibm.com>, "mingo@...e.hu" <mingo@...e.hu>, "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [BISECTION RESULT] sched: revert cpu_clock to pre-27ec4407790d075c325e1f4da0a19c56953cce23 state > Can you guys on IA64 possibly set ar.k3 simply to zero or to some > other similar value which cancels out the per-cpu computation? > > That's what sparc64 and other platforms do. In cpu_init() we set ar.k3 to the base physical address of the percpu area. The alt-dtlb miss handler uses this register to set up a TLB mapping from virtual address 0xffffffffffff0000 to this physical address. This means that most per-cpu accesses are very cheap (as the compiler can use a small -ve offset from register r0 to load the virtual address). Accessing ar.k3 is a bit slow ... so making the per-cpu code use that on every access to a per-cpu variable would be unpleasant. -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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