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authorVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>2005-06-23 00:08:13 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-23 09:45:08 -0700
commit8a9e1b0f564615bd92ba50162623e25c2904e564 (patch)
treeff8fe9b280cc539e4a57826e2dee072d247d284a /include/asm-x86_64
parent0f8e2d62fa04441cd12c08ce521e84e5bd3f8a46 (diff)
downloadlinux-8a9e1b0f564615bd92ba50162623e25c2904e564.tar.gz
[PATCH] Platform SMIs and their interferance with tsc based delay calibration
Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/asm-x86_64')
-rw-r--r--include/asm-x86_64/timex.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/asm-x86_64/timex.h b/include/asm-x86_64/timex.h
index 34f31a18f90..24ecf6a637c 100644
--- a/include/asm-x86_64/timex.h
+++ b/include/asm-x86_64/timex.h
@@ -26,6 +26,9 @@ static inline cycles_t get_cycles (void)
extern unsigned int cpu_khz;
+extern int read_current_timer(unsigned long *timer_value);
+#define ARCH_HAS_READ_CURRENT_TIMER 1
+
extern struct vxtime_data vxtime;
#endif