[POWERPC] Fix mdelay badness on shared processor partitions (1e92a550) · Commits · 戴 / test

On partitioned PPC64 systems where a partition is given 1/10 of a processor, we have seen mdelay() delaying for 10 times longer than it should. The reason is that the generic mdelay(n) does n delays of 1 millisecond each. However, with 1/10 of a processor, we only get a one-millisecond timeslice every 10ms. Thus each 1 millisecond delay loop ends up taking 10ms elapsed time. The solution is just to use the PPC64 udelay function, which uses the timebase to ensure that the delay is based on elapsed time rather than how much processing time the partition has been given. (Yes, the generic mdelay uses the PPC64 udelay, but the problem is that the start time gets reset every millisecond, and each time it gets reset we lose another 9ms.) Signed-off-by:

Anton Blanchard <anton@samba.org> Signed-off-by:

Paul Mackerras <paulus@samba.org> Acked-by:

Andrew Morton <akpm@osdl.org>

include/asm-powerpc/delay.h

+13 −0

Original line number	Diff line number	Diff line
		@@ -17,5 +17,18 @@
		extern void __delay(unsigned long loops);
		extern void udelay(unsigned long usecs);

		/*
		* On shared processor machines the generic implementation of mdelay can
		* result in large errors. While each iteration of the loop inside mdelay
		* is supposed to take 1ms, the hypervisor could sleep our partition for
		* longer (eg 10ms). With the right timing these errors can add up.
		*
		* Since there is no 32bit overflow issue on 64bit kernels, just call
		* udelay directly.
		*/
		#ifdef CONFIG_PPC64
		#define mdelay(n) udelay((n) * 1000)
		#endif

		#endif /* __KERNEL__ */
		#endif /* _ASM_POWERPC_DELAY_H */

include/linux/delay.h

+1 −4

Original line number	Diff line number	Diff line
		@@ -25,10 +25,7 @@ extern unsigned long loops_per_jiffy;
		#define MAX_UDELAY_MS 5
		#endif

		#ifdef notdef
		#define mdelay(n) (\
		{unsigned long __ms=(n); while (__ms--) udelay(1000);})
		#else
		#ifndef mdelay
		#define mdelay(n) (\
		(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
		({unsigned long __ms=(n); while (__ms--) udelay(1000);}))

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