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3dc167ba57
People report that utime and stime from /proc/<pid>/stat become very wrong when the numbers are big enough, especially if you watch these counters incrementally. Specifically, the current implementation of: stime*rtime/total, results in a saw-tooth function on top of the desired line, where the teeth grow in size the larger the values become. IOW, it has a relative error. The result is that, when watching incrementally as time progresses (for large values), we'll see periods of pure stime or utime increase, irrespective of the actual ratio we're striving for. Replace scale_stime() with a math64.h helper: mul_u64_u64_div_u64() that is far more accurate. This also allows architectures to override the implementation -- for instance they can opt for the old algorithm if this new one turns out to be too expensive for them. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200519172506.GA317395@hirez.programming.kicks-ass.net
102 lines
2.3 KiB
C
102 lines
2.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_DIV64_H
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#define _ASM_X86_DIV64_H
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#ifdef CONFIG_X86_32
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#include <linux/types.h>
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#include <linux/log2.h>
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/*
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* do_div() is NOT a C function. It wants to return
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* two values (the quotient and the remainder), but
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* since that doesn't work very well in C, what it
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* does is:
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*
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* - modifies the 64-bit dividend _in_place_
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* - returns the 32-bit remainder
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*
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* This ends up being the most efficient "calling
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* convention" on x86.
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*/
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#define do_div(n, base) \
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({ \
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unsigned long __upper, __low, __high, __mod, __base; \
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__base = (base); \
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if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
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__mod = n & (__base - 1); \
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n >>= ilog2(__base); \
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} else { \
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asm("" : "=a" (__low), "=d" (__high) : "A" (n));\
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__upper = __high; \
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if (__high) { \
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__upper = __high % (__base); \
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__high = __high / (__base); \
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} \
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asm("divl %2" : "=a" (__low), "=d" (__mod) \
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: "rm" (__base), "0" (__low), "1" (__upper)); \
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asm("" : "=A" (n) : "a" (__low), "d" (__high)); \
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} \
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__mod; \
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})
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static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
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{
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union {
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u64 v64;
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u32 v32[2];
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} d = { dividend };
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u32 upper;
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upper = d.v32[1];
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d.v32[1] = 0;
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if (upper >= divisor) {
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d.v32[1] = upper / divisor;
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upper %= divisor;
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}
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asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
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"rm" (divisor), "0" (d.v32[0]), "1" (upper));
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return d.v64;
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}
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#define div_u64_rem div_u64_rem
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static inline u64 mul_u32_u32(u32 a, u32 b)
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{
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u32 high, low;
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asm ("mull %[b]" : "=a" (low), "=d" (high)
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: [a] "a" (a), [b] "rm" (b) );
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return low | ((u64)high) << 32;
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}
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#define mul_u32_u32 mul_u32_u32
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#else
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# include <asm-generic/div64.h>
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/*
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* Will generate an #DE when the result doesn't fit u64, could fix with an
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* __ex_table[] entry when it becomes an issue.
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*/
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static inline u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div)
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{
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u64 q;
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asm ("mulq %2; divq %3" : "=a" (q)
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: "a" (a), "rm" (mul), "rm" (div)
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: "rdx");
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return q;
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}
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#define mul_u64_u64_div_u64 mul_u64_u64_div_u64
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static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div)
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{
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return mul_u64_u64_div_u64(a, mul, div);
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}
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#define mul_u64_u32_div mul_u64_u32_div
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#endif /* CONFIG_X86_32 */
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#endif /* _ASM_X86_DIV64_H */
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