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Message-ID: <20071031093100.3a1542b0@laptopd505.fenrus.org> Date: Wed, 31 Oct 2007 09:31:00 -0700 From: Arjan van de Ven <arjan@...radead.org> To: Andi Kleen <ak@...e.de> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] Use 64bit timer values while calibrating BogoMips On Wed, 31 Oct 2007 16:52:16 +0100 Andi Kleen <ak@...e.de> wrote: > > When calibrating BogoMips 32bit architectures using > read_current_timer will truncate the timer value to 32bit. > This is a problem on x86 when the TSC timer is already beyond > 2^32-1 or wraps during the calibration. The current code > has no wrap handling. > > This could potentially lead to wrong BogoMips, causing > incorrect delays e.g. in hardware drivers and then difficult > to track down bugs. bogomips tends to not be used for that nowadays > > Change read_current_timer() to always return a 64bit > value even on 32bit and do the computation in 64bit. > > Only found by code inspection; i haven't seen a failure > in the wild. > > avr32/sparc64 read_current_timer() updated, but I haven't > compiled/tested them. one general comment, if you really want 64 bit... you're using "unsigned long long" all over, just use u64 instead. -- If you want to reach me at my work email, use arjan@...ux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org - 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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